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Dynamic Skiametry 

in 

Theory and Practice 

Embracing Its Association with Static Skiametry and 

with Those Optometric Methods Wherein the 

Correlation of Accommodation and 

Convergence Must Be 

Considered 

BY 
ANDREW JAY CROSS, D.O.S. 

Author of "A System of Ocular Skiametry." Lecturer on Theoretic and Practical 

Optometry, Columbia University. President American Optical Association 1900-01, 

and Honorary Life Member of Its Scientific Section. President Optical Society 

State of New York 1897-98-99-1900. Dean of The New York Institute 

of Optometry 1907 08-09. Honorary Member Rochester, N. Y., 

and Syracuse, N. Y., Optometric Societies, etc., etc. 



IVith Seventy -One Illustrations 

(Sixty-one of which are Original Drawings) 



PUBLISHED BY 

A. JAY CROSS OPTICAL COMPANY 

20 East Twenty-third Street 
New York 

1911 0j£ v< ^ 



<&* 



\* 



i\1 



COPYRIGHT, 191 1, BY ANDREW JAY CROSS 



Saft. N..Y. State Qptomstric issoc frial* ■»** 



Press of S. L. Parsons & Co. 
45 Rose Street, New York 



To 

My Colleague, 

CHARLES F. PRENTICE, M E., 

One of the First to Recognize the Scientific Value of Dynamic 
Skiametry, and With Whom I Have Been Associated in Cyto- 
metric Organization and Education Work Since 1895, This Little 
Volume is Affectionately Dedicated. 



PREFACE 

The progress made in optometry during the past decade has 
perhaps been influenced by no one division more than it has 
by that of Dynamic, Skiametry, for the revolutionary character 
of this new objective method has of necessity developed many 
minor factors which were unknown when the former book, "A 
System of Ocular Skiametry," was issued. 

For this reason, it is now deemed wise to present new expla- 
nations of the theory and practice of dynamic shadow testing 
and, at the same time, retain all of the old that has been found 
good. 

Static skiametry, or that method known by the blanket term 
"retinoscopy," has been explained so often by other writers that 
it is thought quite unnecessary to add to the length of this little 
volume further than by a brief description of the cardinal 
points involved, hence it will be taken for granted that the 
reader is more or less familiar with the optical principles under- 
lying Bowman's great discovery, and with the added improve- 
ments made by Cuignet and others prior to 1902, when the 
dynamic method was originated and made public by the author. 

New York, 
October, ign. 



PREFACE TO SECOND EDITION 

From one viewpoint it might be deemed unfortunate that 
success in the practice of dynamic skiametry calls for the high 
class skill it does in order to correctly read the shadow's action, 
but from another angle this may be a means of separating the 
competent from the incompetent, for only through consci- 
entious and painstaking effort can adeptness in this work be 
achieved. 

No startling developments have taken place in either the 
theory or the practice of dynamic skiametry since the publica- 
tion of the previous edition of this book. The author, how- 
ever, has changed his views somewhat regarding the correct- 
ness of classifying the difference between the findings by the 
static method and those by the dynamic as being entirely com- 
posed of latent errors, for he now has reason to believe that 
the visual organs in their effort to meet individual require- 
ments adjust accommodation and convergence in a manner 
to give the fusion sense the greatest possible aid. Thus 
exophoria might cause some hyperopia to still remain latent, 
or it might explain why presbyopia is often less than that indi- 
cated by the Donder's table. 

As harmony between accommodation and convergence is an 
essential, it logically follows that the method which objectively 
determines the exact amount of refractive assistance required 
to produce this harmony must be of infinitely greater value 
than those methods where an estimate of the dynamic condition 
is necessarily based upon the uncertainty of static findings. 

Dynamic skiametry is perhaps not all it will be some day, 
but as at present understood it gives a most valuable datum 
to the examiner, and one that is unobtainable by any other 
known, dependable means. It is therefore very gratifying to 
note the increasing numbers of those who are now recognizing 
this merit. 

New York, January, 1915. 



CONTENTS 



CHAPTER I Pages 15 to 26 

Ocular Skiametry as a System, Its Value in Optometry and the 
Optical Knowledge Necessary to Master It, Including Difficulties 
to be Overcome. 

CHAPTER II Pages 27 to 46 

Proper and Improper Examination Rooms, Size Intensity and 
Control of Illumination, the Plane Skiascope, How to Handle 
It, and Some Novel Inventions. 

CHAPTER III Pages 47 to 59 

Schematic Eye Practice and Its Importance to Students, Model 
Eyes and the Exercise of Care in Their Adjustment. Reduction 
and Transposition of Lens Values, and the Necessity for the 
Complete Mastery of This Work in Successful Skiametry. 

CHAPTER IV Pages 60 to 79 

Why Ocular Pupils Appear Red When Viewed Through a Skia- 
scope, With a Brief Description of the Cardinal Points Involved 
in Static Skiametry as Practiced With the Plane Mirror, Includ- 
ing Some Theories Regarding Fundus Reflex. 

CHAPTER V Pages 80 to 99 

Theory of Dynamic Skiametry, and the Importance of Reliable 
Fixation in Co-ordinate and Independent Observation, With a 
Reference to Three Essential Myopias, and an Explanation of 
"Ray Values". 

CHAPTER VI Pages 100 to 114 

Orthophoric and Heterophoric Conditions, and the Influence of 
Habit Upon Accommodation and Convergence, With Special 
Consideration of Spasms and the Use of Prisms. 

CHAPTER VII Pages 115 to 123 

Practice of Dynamic Skiametry, Its Use in Measuring Regular and 
Irregular Astigmia, and Its Special Value in the Objective Esti- 
mation of Presbyopia and Sub-Normal Accommodation, To- 
gether With Its Relationship to Other Methods and Tests. 



CONTENTS— Continued 

CHAPTER VIII Pages 124 to 137 

Illustrative Cases, Showing the Comparative Value of Static and 
Dynamic Skiametry in Patients of Different Ages, Occupation 
and General Physical Condition. 

CHAPTER IX Pages 138 to 152 

Multiple Methods in Optometry and Their Value in Corroborative 
Measurements, the Systematic Keeping of Records and the Im- 
portance of "Case History", Including Resourcefulness and 
Mechanical Mydriasis. 

CHAPTER X Pages 153 to 172 

Value of Instruments in Practising Optometry. Mobile and Unit 
Lens Systems, Various Instruments Used in Skiametry, With 
Description of Their Mechanical Construction. 

CHAPTER XI Pages 173 to 196 

Questions and Answers Pertaining to Static and Dynamic Ski- 
ametry and Correlated Subjects. With Pertinent Remarks Em- 
phasizing the Salient Points Involved. 

CHAPTER XII Pages 197 to 218 

Opinions of Others Regarding the Value of Skiametry in General 
and the Dynamic Method in Particular, With Comments on 
Objective Versus Subjective Optometry, and the Relationship of 
Accommodation and Convergence, Including Quotations on 
Mental Perception, and an Epilogue. 



ILLUSTRATIONS 

Fig. Page 

i Parallel rays of light converged 20 

2 Divergent rays of light paralleled. 20 

3 Acetylene gas lamp with metal chimney 30 

4 Asbestos lined metal chimney 31 

5 Asbestos lined glass chimney 32 

6 Asbestos-paper chimney-cover with iris diaphragm opening. . 33 

7 Spiral filament in electric lamp 34 

8 Author's asbestos covered electric lamp 36 

9 DeZeng electric retinoscope 37 

10 The "Hardy" wall bracket for gas or electric lamp 38 

11 A simple skiascope 40 

12 Author's double bracket skiascope 41 

13 Skiametric fixation card 42 

14 Skiametric fixation card 42 

15 Manner of holding author's skiascope 43 

16 Reisner's retinoscope 45 

17 Klein's retinoscope 46 

18 DeZeng-Standard schematic eye 48 

19 Queen's pasteboard schematic eye 49 

20 Two cylindric lenses of unequal focus and axis 52 

21 A crossed cylinder-lens of unequal meridional focus 53 

22 Three cylindric lenses of equal focus, one at axis 90, and two 

at axis 180 53 

23 One crossed cylinder of equal meridional focus and one 

simple cylinder at axis 180 54 

24 Crossed cylindric lens of plus and minus curvatures 57 

25 Three cylindric lenses, two plus and one minus 58 

26 Illumination of second card through hole in first one 61 

27 Return rays from second card entering eye through tube in 

candle 61 

28 Substituting a skiascope for candle tube 62 

29 Illuminating the ocular fundus 64 

30 The illuminated area on the fundus. 65 



ILLUSTRATIONS— Continued. 
Fig. Page 

31 Rays returning from edge of illuminated area on the fundus. . . 65 

32 Returning rays influenced by a convex lens 66 

33 Why the shadow moves "with" the mirror 67 

34 Why the shadow moves "against" the mirror 68 

35 Pupillary appearance of a so-called "shadow" 69 

36 Why the retinal illumination is larger in ametropia than in 

emmetropia 74 

37 Why shadows move slower in ametropia than in emmetropia.. 75 

38 Why a shadow is duller in myopia than in a like degree of 

hypermetropia 76 

39 Relative size of retinal illumination in high and low degrees 

of myopia 77 

40 The optical principles of penumbra 77 

41 The optical principles of penumbra doubled 78 

42 Interference of penumbra in shadow testing 79 

43 True myopia ( Static Method) 84 

44 Artificial myopia (Static Method) 85 

45 Accommodative myopia (Dynamic Method) 86 

46 How the accommodation can absorb a ciliary spasm 88 

47 Multiple fixation and observation points 91 

48 Author's fixation stand 92 

49 Fixation stand target card 93 

50 Reverse side of fixation card 93 

51 Position for initial examination 94 

52 Balancing the accommodation and convergence in emmetropia. 104 

53 Equal innervation necessary to balance accommodation and 

convergence in emmetropia 105 

54 Imbalance of accommodation and convergence in hyperme- 

tropia 106 

55 Unequal innervation required to balance accommodation and 

convergence in hypermetropia 106 

56 Imbalance of accommodation and convergence in myopia.... 107 

57 Unequal innervation required to balance accommodation and 
convergence in myopia 107 



ILLUSTRATIONS-Continued. 

Fig. Page 

58 Author's record blank 145 

59 Regular size pupil 151 

60 Area of magnified pupil 151 

61 Refraction by lenses placed close together 154 

62 Refraction by lenses separated 155 

63 King's binocular hand trial set 156 

64 Skiametric lens rack of Wurdemann 158 

65 Lens disc used by Crain and others 159 

66 Standards "Umbrameter" 160 

67 The Meriden "Oculometroscope" 162 

68 The "Geneva" retinoscope 164 

69 DeZeng*s Optometer, Phorometer and Skiameter 167 

70 Constructive principle of the author's skiameter 170 

71 Author's skiameter without base 171 



Dynamic Skiametry 

in 
Theory and Practice 



CHAPTER I. 

Ocular Skiametry as a System. — Its Value in Optometry 
and the Optical Knowledge Necessary to Master It, 
Including Difficulties to be Overcome. 

SKIAMETRY AS A SYSTEM. Formerly there was 
only one method employed in measuring eyes by the so-called 
shadow test, and this one method was made to do service for 
the six-year-old child and the sixty-year-old adult. 

This one method was also employed for measuring the 
myope of high degree and the hypermetrope of low. Long 
standing habits of suppression of accommodation or conver- 
gence, due to impaired co-ordination, were entirely ignored and 
presbyopia was never a factor to be considered. Indeed, all 
eyes, like all Chinamen, were said to "look alike." 

It is not many years since eminent authorities claimed 
that the recognition and correction, with lenses, of hyperopic 
errors of less than one diopter was equivalent to taking an un- 
fair advantage of a patient, and therefore savored of charletan- 
ism. What is now known as eye strain was classified as latent 
hypermetropia and of trifling importance unless of high degree. 

But the foreword in optometry, particularly during the past 
few years, has been to pay more attention to minor details for, 
as in other walks, both service and comfort are often secured by 
giving heed to the little things. This care and attention has 
developed the fact that greater accuracy in shadow testing can 
only be obtained by applying methods which take into consid- 
eration the patient's age, and other previously overlooked factors 
requiring varying procedure in varying cases. 

The word "system" is defined as "a series of methods." so 



1 6 SKIAMETRY AS A SYSTEM 

it is easy to understand why ocular skiametry or, literally, eye- 
shadow-measuring, came to be known as a system of ocular 
skiametry, 

VALUE OF SKIAMETRY. In the general practice of 
his profession the most difficult problem that confronts the 
optometrist is the fitting of his patient's preconceived notions 
as to the kind of glasses needed, and the manner in which they 
are to be worn, so in attempting to make plain the true value 
of static and dynamic skiametry the problem which confronts the 
writer is the overcoming of the previously formed opinion that 
most readers have, for many inquirers into the merits of 
shadow testing seem to be possessed with the belief that every 
case which presents itself is capable of being both easily and 
accurately refracted by means of Bowman's great discovery. 
This expectation being as inconsistent with the real facts as it 
would be to expect like results from trial case tests or by any 
other one optometric method. 

The truth can perhaps be fairly expressed by saying that 
shadow testing bears to trial case testing much the same rela- 
tion that the addition of a column of figures from the top bears 
to its addition from the bottom. 

Skiametry will uncover at a single sitting optical conditions 
which it would be quite impossible for ordinary trial case tests 
to do. On the other hand, the latter will show visual conditions 
of which the former can tell nothing. Viewed again from a 
similar position we find that the two general methods for esti- 
mating ocular errors of refraction, known by the terms objective 
and subjective, are like seeing for one's self and taking the 
testimony of others. Usually either method is fairly 
reliable in ordinary cases, but in extraordinary ones — the kind 
that make and break reputations — the evidence can be none 
too corroborative. 

So we find skiametric and trial case testing to be inter-de- 
pendent, both systems having their weak and strong points, and 



VALUE OF SKIAMETRY 1 7 

one aiding in the judgment requisite for the successful applica- 
tion of the other, skiametry coming first because it is the great 
refractive pilot, or pathfinder, and because, too, there are many 
conditions, other than errors of refraction, that are shown up 
by its use and which, if it were not for this early use, might 
needlessly prolong an otherwise short examination. 

It is hoped, therefore, that this point is made clear regard- 
ing the value of shadow testing. It is deemed of no more nor 
less value than the trial case test, and that neither one is 
infallible, and that both are absolutely essential in all prime 
cases, whether the results obtained by either coincide with those 
of the other or not, for this very lack of coincidence is often the 
key which enables a trained judgment to solve a refractive 
riddle. 

By basing their judgment upon the principle that the proof 
of the pudding lies in interviewing the one who has chewed the 
string, some credulous inquirers have been led to estimate the 
merits of shadow testing by taking the testimony of those who 
have falsely pretended to possess a thorough knowledge of it r 
and this unreliable information has led them to believe that if 
skiametry is faulty in some hands it must be faulty in all. 
Whereas the reverse reasoning would in all probability be pro- 
ductive of better results, for that which one can achieve by 
study and practice it is quite possible for others to achieve by 
equal application and effort, and sometimes by even less where 
assistance is given by skilled instructors. 

For nearly four decades the ablest optometric researchers 
have striven their utmost to find a better objective means than 
skiametry for determining the optical condition of eyes, but so far 
without avail. And judging from the present advanced knowl- 
edge regarding optics and optometry it is pretty safe to say that 
the shadow test is here to stay, for a long time at least, and that 
those whose duty it is to adapt glasses to the eyes of others will 
find their work more reliable and much easier if they will take 



l8 OPTICAL KNOWLEDGE NECESSARY 

the time to thoroughly master this valuable means for ascertain- 
ing ocular refractive conditions in a manner independent of the 
patient's intelligence. 

Now this phrase, "independent of the patient's intelligence," 
may prove somewhat misleading, since even those who are 
experienced in skiametric work find many cases in which the 
results obtained are very unsatisfactory indeed. Yet, when an 
examiner measures a case by skiametry and notes an error of 
refraction which later on is confirmed by the trial case test, he 
feels that he has received advance information of a truly "inde- 
pendent" character, and upon which he can rely with greater 
confidence than if this information had been denied him. On 
the other hand, if the trial case test does not confirm the mirror 
findings, then the mirror is employed again to confirm the trial- 
case findings. The subjective is used to check the objective, and 
then the objective again to corroborate the subjective. 

OPTICAL KNOWLEDGE NECESSARY. Expressed in 
a broad way, the optical knowledge necessary to achieve skia- 
metric success is all the optical knowledge a student can obtain. 
But keeping in mind the practical side of the work there will 
be found a few essentials which are clearly indicated before 
intelligent progress can be reasonably expected. 

The general optical principles of the shadow test in its 
simplest form are not very complicated. Taken, however, in 
connection with its optometric associates skiametry represents, 
as a whole, a rather high order of knowledge regarding both 
physical and physiologic optics. It also requires in its applica- 
tion a certain amount of skill or dexterity in the manipulation of 
indispensable mechanical devices, such as the skiascope and ski- 
ameter, no matter whether the latter be a simple trial frame with 
test lenses, or a more elaborate and useful apparatus. 

There are two leading accomplishments in shadow testing 
in which an examiner must be proficient before he can achieve 



OPTICAL KNOWLEDGE NECESSARY 19 

success^ The first of these is the control of the reflected light 
and the determination of the direction of the shadow's motion, 
under both favorable and unfavorable conditions. The second 
lies in being able to add and subtract known refractive lens 
quantities and to tell with precision what their ray-bending 
value is at all distances from an eye under examination. To 
express it tersely then, an examiner must be able to detect any 
action of the shadow and to know exactly what the optical value 
of this action is when influenced by either lenses or fixation. 

The first of the above requirements can be gained by daily 
practice, but the second requires considerable study and applica- 
tion, as it involves a knowledge of angles of light, or ray values, 
as well as of refraction, or lens values. 

When a patient's eye is considered as an object, instead of 
as a subject, then its refractive condition must be determined by 
noting the behavior of the light reflected from the retina as it 
leaves the eye, and methods of procedure known as objective 
must therefore be applied. 

Many students of optics who have confined their efforts to a 
mastery of subjective optometry alone often find themselves 
quite at sea when they undertake objective methods. And the 
reason for this usually lies in the fact that they have given 
attention to the subject of light as it travels in but one direction, 
namely, as it enters an eye. 

One of the foundation principles taught in optical text-books 
is that light returns over the same course which it has traveled, 
hence if parallel rays of light are made to pass through a convex 
lens they will come to a focus at the so-called "strength" of the 
lens. Invert this order, by placing a lighted candle at the focus 
of the lens, and the rays of light will diverge until they pass 
through the lens, after which they will be parallel. See Figs. 
1 and 2. 

In shadow testing the retina of an eye is the apparent source 
of light, although in reality the retina is only a poor quality of 



20 



OPTICAL KNOWLEDGE NECESSARY 



mirror which reflects the light thrown into the eye by the skia- 
scope. This illumination, or reflection, behaves like a piece 
of red flannel, or any other visible object which acts as a high 
or low grade mirror according to its ability to reflect light. 
Glass with amalgam backing, and polished metals being of the 
highest order, while lampblack and black velvet are of the 
lowest. 

Fig. i. 




Focus. 



Lens 
PARALLEL RAYS OF LIGHT CONVERGED. 



Fig. 2. 




U^J Lens 

DIVERGENT RAYS OF LIGHT PARALLELED. 



The correlation of accommodation and convergence is an- 
other subject which students of ocular skiametry must under- 
stand in order to do their work intelligently. Thus it will be 
seen that skiametric proficiency involves a pretty thorough 
grounding in something more than rudimentary optics. With 
the elimination of the use of the concave mirror, however, and 



DIFFICULTIES TO OVERCOME 21 

by the aid of modern apparatus it is now possible to dispense 
with many details which formerly resulted in the confusion of 
beginners. Still, notwithstanding this, a student will find much 
that will call forth his best efforts before he can feel assured of 
the reliability of his findings. 

It is one thing to master ocular skiametry under regular 
conditions and quite another to rightly differentiate the irregu- 
lar and apply that judgment which secures success. But, as 
in other studies, the deeper the student delves the more he finds 
to learn, and the easier do the foundation principles become. 
The wise searcher after optical facts, which in the aggregate 
constitute optical knowledge, will first learn the A, B, C of 
light and lenses, together with the reduction and transposition 
of the latter, and next he will master physiologic optics, in addi- 
tion to the art of subjectively correcting with lenses any mani- 
fest conditions which may be met. The student may then be 
said to possess sufficient optical knowledge to begin the study of 
ocular skiametry with a fair chance of achieving success. 

DIFFICULTIES TO OVERCOME. The stumbling 
blocks in ocular skiametry are not few, and they seem to grow 
apace as the system becomes perfected in its many details. The 
first great obstacle which usually presents itself is place, or 
examination room. The medical refractionist who takes up 
this work may already be provided with a regulation dark- 
room for his ophthalmoscopic work, and in this room he at- 
tempts to practice successful skiametry. The conditions being 
poor, he gets poor results and abandons the work in the belief 
that shadow testing is sadly overrated. 

The non-medical refractionist may possibly go to the other 
extreme. The specious plea that a dark room is unnecessary 
is listened to, then not being able to use a cycloplegic, and 
having a knowledge of the static method only, he wonders why 
his skiametric work varies so with his trial case findings. And 



22 DIFFICULTIES TO OVERCOME 

then, too, because he possesses a sufficient degree of skill to feel 
comparatively sure of the action of the shadow in an occasional 
case, he either blames the system or virtually condemns it by 
faint praise. 

Next to a poorly-arranged examination room in point of dis- 
couragement with shadow-testing comes an inadequate source of 
illumination. Almost any lamp, whether electric, gas or oil, 
looks to a novice as though it ought to prove of sufficient in- 
tensity to determine a shadow's action, because when the light 
is reflected into a naked eye the fundus reflex seems fairly 
bright, but by placing a lens or two in front of this eye, or by 
permitting the patient to look in an unfavorable direction, such a 
pronounced diminution will often be produced, in the definition 
of the shadow, as to render accurate work impossible. 

Even where the source of illumination is fifty-candle power, 
or more, the experienced examiner will meet with cases where 
the deeply pigmented retina gives back so poor a reflection that 
only the greatest care and skill can determine the action of the 
shadow. 

There is a vast difference in general illuminating power 
between a flame that is hooded so as to show only a small 
aperture and one that is not, for a dark-room light to be satis- 
factory must not be too large. Its apparent intensity should 
resemble the "glory-hole" of a furnace, and then if this should 
prove too bright for an occasional supersensitive eye it can 
always be diminished by moving the patient farther away 
from it. 

The law that light decreases in proportion to the square of 
the distance at which it is used, enables a light intensity equal 
to sixty-candle power at two feet away to be decreased to fifteen- 
candle power by withdrawing to a distance of four feet. Thus 
it will be seen that with a powerful source of illumination an 
examiner can readily reduce it to almost any candle power he 
desires. 



DIFFICULTIES TO OVERCOME 23 

Just how high a candle power the human eye can bear with- 
out doing it injury varies, undoubtedly, with individuals and 
the duration of the exposure. A hundred-candle power lamp 
hooded so that only a limited portion of its general radiant 
energy is available could probably be comfortably borne by the 
average eye under ordinary skiametric conditions for several 
minutes, whereas the length of time for a proper measurement 
is only a matter of seconds. Too bright a light therefore need 
not be feared when the patient does not look directly at the 
reflection in the mirror. 

In using a bright light, however, there is one thing an 
examiner should always remember, as it can properly be classi- 
fied among the stumbling blocks to be avoided, and that is to 
never allow himself to look directly at the source of his illumina- 
tion prior to or during an examination. The reason is that the 
sensitiveness of his own retina is such as to retain the im- 
pressions made by a bright light to such a degree that duller 
objects cannot be clearly seen for several minutes thereafter, 
and, as a consequence, if an examiner permits himself to look 
directly at his lamp for an instant or two and then tries to use 
his mirror he will find it very difficult to detect the dull outline 
of the shadow, or note its action. If an inspection of a lamp is 
necessary to determine its condition, or distance away, it is a 
wise examiner who will derive his information by looking a few 
inches to one side of the flame and not directly at it. 

Another stumbling block in the road to skiametric success 
lies in corroded, soiled and dusty mirrors, especially at the edge 
of the so-called "peep-hole" of the skiascope. Every examiner 
should possess at least two or more of these instruments, so 
when one gets out of order it can be sent to the factory for re- 
silvering. Mirrors, to give the best service, must not be of too 
great a diameter, nor must their peep-holes be large or bored 
through the glass. Consequently these peep-holes, which are 
really not holes in the strict sense of the word, but round spots 



24 DIFFICULTIES TO OVERCOME 

of clear glass, made by scraping off the silver of the mirror, must 
be kept immaculately clean so as to prevent particles of dust 
from interfering with the free passage of light, or else the 
shadow's action will be perceptibly dimmed. 

One of the underlying causes of the success achieved in 
many branches of modern science is undoubtedly due to ultra- 
cleanliness and attention to details, and so it will be with 
advanced optometry as regards details, for dealings with imag- 
inary quantities of elastic ether, as light is termed, call for 
extreme care on the part of the examiner, if he is of the kind 
that will be satisfied with nothing short of the highest attain- 
ment. 

A thorough knowledge of lenses is still another important 
factor, as there is probably no one study connected with a skia- 
metrist's educational equipment which demands a more perfect 
mastery than does that of the reducing, transposing and com- 
bining lens values. In his desire to attain perfection on the 
practical side of adapting glasses to the eyes of others, the stud- 
ent is apt to pass hurriedly by the dry underlying optical prin- 
ciples upon which lenses are based and, as a consequence, after 
his first few years of "success in every case" his desire to climb 
higher is interfered with through his lack of knowledge of that 
which he ought to have learned at the beginning of his optical 
career. 

In ocular skiametry a simple stumbling block to many 
students is their inability to tell what the true refraction of their 
patient's eye is, when it takes an ordinary lens quantity of, say, 
one diopter to reverse the shadow in one meridian, while only a 
half-diopter is required to reverse it in the meridian at right 
angles to this. Especially is this true where the axes happen to 
be oblique, or where one lens is plus and the other minus. 

Now this is all wrong, for if an optometrist ought to know 
anything he ought to know all about lenses — how they are made, 
what index of refraction and spherical aberration mean, wherein 



DIFFICULTIES TO OVERCOME 2$ 

cylindrical, spherical and ellipsoidal curvatures differ and, above 
all, the very best way to combine lens quantities in order to 
produce the highest degree of central and peripheral vision, 
together with angle and decentration for the relief of strain and 
the production of comfort. 

A thorough knowledge of light and lenses is the great key 
to the achievement of skiametric success. After a student has 
learned all about the physical side of refractive work the phys- 
iologic becomes easier, just as a mathematician who has skipped 
some fundamental principle finds his higher work puzzling, but 
where he has covered his ground carefully then his advance- 
ment is less difficult. 

A very few sittings will give a student the mastery of a 
skiascopic mirror and enable him to tell the movement of the 
pupillary shadows, but how to control these shadows by the aid 
of lenses combined with fixation, and to know the real optical 
value of the refractive power used, is where one of the greatest 
of the stumbling blocks in shadow testing lurks, so that those 
who become discouraged in their skiametric efforts must not 
blame this grand test, but look, rather, to their own weakness in 
their lack of adequate optical knowledge and skill. 

There is one more point to which attention should be di- 
rected, although it can hardly be called a "stumbling block," 
even though in some cases it seems to act as such. It pertains 
to an examiner's own vision, which should be such as to enable 
him to see with definition a moderately pale shadow on a pink 
background at a distance of at least forty inches. Therefore all 
examiners having myopia should have their own refractive 
errors corrected to within less than one diopter before they 
attempt skiametric work. All hypermetropes, on the other hand, 
whose amplitude of accommodation at thirteen inches is less than 
their error of refraction must also wear their correcting lenses 
before they can make satisfactory shadow tests, and this applies, 
too, to presbyopes who should wear their reading correction 



26 DIFFICULTIES TO OVERCOME 

when using the mirror at near points. It would seem, 
however, that the peep-hole in a skiascope ought to act as a 
pinhole test and give an examiner good vision no matter what 
his refractive error might be, but experience, that great teacher, 
rules it otherwise in those cases where high-class results are 
sought for. 

Some examiners have found difficulty in keeping the peep- 
hole of a skiascope exactly in front of their fixing eye, and thus 
obtaining a good reflex. This is usually due to their inability to 
close the unused eye, hence practice in this respect is important, 
for if one eye is in use the other should be occasionally closed 
in order to make sure that the fixing eye is properly located. 



CHAPTER II. 

Proper and Improper Examination Rooms. — Size, Inten- 
sity and Control of Illumination. — The Plane Ski- 
ascope, How to Handle It, and Some Novel Inven- 
tions. 

EXAMINATION ROOMS. Since the fitting of glasses 
"over the counter" has practically passed away, the considera- 
tion of where the fitting should be done is now in order. 

To describe an ideal examination room is quite a different 
matter than it is to attempt the description of an adequate apart- 
ment that might serve fairly well as a place in which to prac- 
tice ocular skiametry. 

The complaint which is frequently heard from many who 
attempt to do refraction work without having suitable place and 
apparatus is that they lack the requisite space, whereas an 
examination of the store or office by one experienced as to re*- 
quirements might lead to the discovery of quite a number of 
places which could be rendered available by the use of properly 
strung wires for hanging light-proof curtains, and which could 
also be made decorative in appearance. Then, too, many are 
persuaded that an examination room must be of Egyptian dark- 
ness, without ventilation, where both examiner and patient will 
be very uncomfortable, especially during warm weather. 

Now this is a wrong conception. An adequate examina- 
tion room needs to be of only semi-darkness, in fact if it is just 
light enough to make the headlines of an ordinary newspaper 
discernible at midday it will be found dark enough for all opto- 
metric purposes. The "Mahomet and the mountan" principle 
can be made use of by increasing the intensity of the light 



28 EXAMINATION ROOMS 

source, instead of making the room appear as dark and gloomy 
as the interior of a hearse. 

The space occupied need not be very wide. The length of 
room, however, ought to be at least twenty feet, but where this 
distance cannot be obtained a length of ten feet can be made to 
appear as twenty by the use of an ordinary wall mirror, test 
cards with reversed letters being placed over the head of the 
patient in a position where their reflection can readily be seen in 
the mirror. 

The ventilation should be perfect, and the space ought to 
contain several chairs for the use of those who accompany the 
patient, while the surroundings should be made as cheerful as 
possible by means of rugs, pictures, etc. 

Both objective and subjective tests should be used without 
having to move the patient from the chair in which he is first 
seated, it being better to bring all instruments and devices to the 
patient rather than require the patient to go to them. 

First impressions are said to be lasting, so that if patients 
are shown into apartments that look as though they were in- 
tended for optometric purposes their confidence is more than 
half won. 

There is a fitness of things, and those whose practice is in 
accord with this ''fitness" generally have occasion to feel satis- 
fied with the results obtained from having given attention to the 
details of environment. Indeed, it has already been said by 
many that next to professional knowledge and skill a well 
appointed examination room is the very best kind of an adver- 
tisement an optometrist can have. 

SOURCES OF ILLUMINATION. The reader's atten- 
tion is called to the importance of using a proper source of 
illumination in order to succeed in shadow testing. Therefore 
it will be the purpose here to describe, with the assistance of 
drawings and photo-reproductions, some of the various lamps 



SOURCES OF ILLUMINATION 2Q, 

employed for this purpose, and to offer criticisms regarding the 
advantages and disadvantages consequent upon their use. 

Practising skiametry by means of a schematic eye is very 
easy in comparison to practising it upon a living eye, for with 
a model eye almost any kind of light will answer, but not so 
with the living organ where the light source should resemble the 
glow emanating from the "glory-hole" of a furnace. 

Oil lamps of all types, while many are magnificent for gen- 
eral lighting purposes, fall away below the standard of efficiency 
when employed for general skiametric uses. The draught in 
almost all lamps is an important factor, and as metal chimneys 
cannot be easily made to take the place of glass ones, on account 
of the transparent aperture which is required opposite the 
flame, it has been found necessary to either line or cover all 
glass chimneys with an opaque substance which extreme heat 
cannot affect. But even where the chimney is lined with a white 
pigment it still falls short of giving satisfaction as an efficient 
illuminator, although the maker may claim that his lamp has 
a general efficiency of over one hundred-candle power. 

The reason for the shortcomings of oil lamps, even those 
using a so-called "flame spreader," is due, no doubt, to the fact 
that the flame, though large, is apt to be very low, and when 
its general intensity is hooded down to the size of a two or 
three centimeter aperture, which is necessary in order to obtain 
good results with a plane mirror, the flame is found of insuf- 
ficient brightness to meet an examiner's needs. 

Perhaps some day some inventive mind will devise a con- 
densing reflector which will permit of hooding the light of oil 
lamps down to a small aperture and at the same time obtain the 
requisite intensity of illumination, but as yet this has not been 
achieved. 

Next to oil comes gas. And here the field of illumination 
broadens, thanks to the inventors of the "Argand" and "Wels- 
bach" burners, and to the gas-generating qualities of naphtha 



30 



SOURCES OF ILLUMINATION 



and of acetylene. Ranking above oil burners comes the Argand 
gas lamp, which also requires a draught to make it burn prop- 
erly, hence a glass chimney is necessary for its use. 

But while the Argand gas lamp is vastly superior to oil 
lamps in general, it is still somewhat below the required stand- 
ard of efficiency, even when working at its best. The flame has 
a yellowish white appearance and seems, like the flame of an oil 

Fig. 3. 




ACETYLENE GAS LAMP WITH METAL CHIMNEY. 



lamp, to lack the illuminating energy necessary to meet modern 
skiametric needs, although in favorable cases fair work can 
sometimes be done by its aid. 

Acetylene lamps represent another style of gas burners which 
in point of intensity of illumination can probably hold their own 
against all competitors. The style shown in Fig. 3 represents a 
portable type. 



SOURCES OF ILLUMINATION 



31 



This lamp is similar in appearance to an ordinary table lamp, 
with the exception that it has an asbestos lined metal chimney. 
It is commercially named an "Electrolite gas lamp," and uses 
pulverized calcium carbide. Its use is endorsed by the board of 
fire underwriters, and it is easy to care for. The light it gives 
is over fifty-candle power, while the expense of maintaining it is 
only about one cent an hour. 

Fig. 4. 



ASBESTOS LINED METAL CHIMNEY. 



Skiametrists are certainly to be congratulated on the inven- 
tion of this lamp, especially those who are compelled to do work 
away from their properly appointed examination rooms, for as 
a portable lamp it is very satisfactory. 

In point of brilliancy, reliability, cost of maintenance and 
ease of adjustment, however, no gas lamp is superior to the 



32 



SOURCES OF ILLUMINATION 



Welsbach type, especially with a metal asbestos lined chimney, 
as shown in Fig. 4. 

This burner is of the "Incandescent" kind wherein chimney 
draught, as with oil burners, is not so much of a factor. A glass 
chimney, however, gives better results than a metal one does, due 
to the fact that the light aperture is covered, thus preventing an 
inrush of air which can interfere with the white heat of the 

Fig. 5. 




ASBESTOS LINED GLASS CHIMNEY. 



mantle. Figs. 4 and 5 show two patterns of chimneys, one metal 
and the other glass, which can be used on the same style of 
burner. 

The Fig. 5 chimney being further away from the mantle, the 
sides do not get as hot as in the pattern shown in Fig. 4, which 
is made in both glass and metal. But the smaller the chimney 
the more convenient is the adjustment of the light, the source of 



SOURCES OF ILLUMINATION 



33 



illumination being nearer to the surface, therefore Fig. 4 is to be 
preferred. 

In Fig. 6 is shown an asbestos paper chimney cover, with 
iris diaphragm opening. This cover can be used outside of an 
ordinary glass chimney, and serves the purpose of a light screen 
very well, although it has the faults of the chimney shown in 

Fig. 6. 




ASBESTOS PAPER CHIMNEY COVER WITH IRIS DIAPHRAGM 
OPENING. 



Fig. 5 as to size. The iris diaphragm, also, seems to be an 
unnecessary arrangement, for it is the size of the skiascopic 
mirror that regulates the facial area of illumination and not 
the size of the chimney aperture, unless a condensing lens is 
used, which would indeed be troublesome. 

The Welsbach lamp gives an ideal light for shadow testing, 



34 SOURCES OF ILLUMINATION 

as its flame is bluish-white, while its intensity is ample, espe- 
cially when its mantle is evenly heated to incandescence. The 
one unfavorable criticism which can be made regarding it is the 
fragile character of its mantles, which are easily injured or de- 
stroyed. But fortunately these mantles are inexpensive and are 
not difficult of adjustment. 

In connection with naphtha, or gasolene, the Welsbach 
burner can also be used, but while the light obtained is not 
as satisfactory as where so-called "City" gas is employed, yet 
the results secured are vastly superior to the use of oil. The 
general use of gasolene has its disadvantages, resulting from its 
explosive qualities. This is a question, however, on which the 

Fig. 7. 




SPIRAL FILAMENT IN ELECTRIC LAMP. 

makers of gasolene lamps and the fire insurance companies are 
not at all in accord. But as efficient illuminators for skiametric 
uses, gasolene lamps, using the Welsbach type of burners, will 
be found more satisfactory than oil, provided they are kept in 
perfect order. 

Wood alcohol is now being extensively used for lighting and 
heating, so there is every reason to believe that lamps suitable 
for optometric purposes will soon be devised where this illumi- 
nant can be employed. 

Electric lamps of the general house-lighting variety, with 
long carbon filaments, are perhaps among the most unsatisfac- 
tory of all illuminators for use in connection with ocular ski- 



SOURCES OF ILLUMINATION 35 

ametry, no matter whether the glass bulbs are of the clear or 
the frosted variety. 

An electric lamp, to be of service in this work, must have 
its filament in compact form, similar in shape to the coils of a 
watch hairspring. Then the light energy of the carbon wires 
when heated to incandescence can be concentrated, and the 
results obtained made superior to the mantle type of gas lamp. 
Fig. 7 shows an electric lamp filament of the spiral kind referred 
to. This lamp needs to be handled with great care, since owing 
to the size and brittle character of its filament it becomes easily 
broken by a sudden jar, or through rough handling in the mail, 
or when shipped by express. 

Fig. 8 shows this same lamp with its glass bulb coated with 
a thick asbestos pigment, leaving a one-inch aperture in its side 
through which the light can emerge. 

This lamp is rated at fifty-candle power and gives a mag- 
nificent reddish white light. The white hot filament, or carbon 
wires, generate considerable heat which, of course, will melt 
the rubber or composition socket handle if the lamp happens to 
be used upside down. The heat from one of these lamps has 
been known to char the curtain hangings of a window, with 
which it came in contact. But used as it is intended to be used, 
this style of lamp certainly supplies an adequate illumination for 
any kind of examination room, whether light or dark, or where 
gas cannot be obtained, such as in modern office buildings, but 
once used, an examiner is rarely ever satisfied with any other 
form of lamp. Most high candle-power lamps, however, are 
somewhat expensive and burn out easily, they should therefore 
never be burned for long periods of time but be turned off and 
allowed to cool as frequently as possible. A snap switch in 
place of the ordinary socket key should be used, and a lamp 
ought never to be burned on a current that is of a higher voltage 
than that for which the lamp is made. 

Attention to these details will often prolong the life and serv- 



36 



SOURCES OF ILLUMINATION 



ice of a lamp two or three-fold, for when the inside of the 
lamp bulb shows a reddish deposit on the glass it indicates de- 
composition of the carbon filament, due to overuse, or abuse of 
some kind. 

Fig. 8. 




AUTHOR S ASBESTOS COVERED ELECTRIC LAMP. 

The cost of maintenance of an electric lamp, too, is some- 
what higher than the mantle-type of gas lamp, and its durability- 
is not as great. Any increase in current, even of only a few 
volts, such as frequently occurs in cities where it is intensified 
at sundown, serves to shorten the life of a lamp very mate- 
rially. These uncertainties of current can be controlled by what 
are called resistance attachments, or rheostats, if an examiner 
cares to incur the expense. The superior light given by these 
high candle-power electric lamps, however, more than com- 
pensates for the trouble and expenditure their use entails. 

Another form of electric illumination, and one which has the 
added advantage of portability, is the combined lamp and mir- 
ror, known as the luminous type of retinoscope. Fig. 9 illus- 
trates the appearance of a late model of one of these instru- 
ments, for which the makers put forth the following claims : 



SOURCES OF ILLUMINATION 



37 



"This self-contained Electric Retinoscope, Fig. 9. 

combining as it does the battery, lamp, mir- 
ror and illuminated fixation letters, leaves 
nothing to be desired in an instrument of 
this kind. It offers tremendous advantages 
in every branch of Retinoscopy. It can be 
used in any place or position irrespective of 
circumstances. 

"The Jumbo Handle Battery shown is 
designed to meet the demand for a very 
compact and portable instrument of maxi- 
mum endurance. It is made of aluminum 
and is designed to hold a two-cell battery of 
regular stock size. This handle is well pro- 
portioned, is convenient to hold and has a 
compressible circuit breaker conveniently 
located for the thumb of the operator. It 
is arranged for either a touch or a fixed 
contact, the lamp being lighted either by 
pressing the extending arm against the 
handle or swinging it around in contact with 
the clip on the top of the cap as desired. 

"The Illuminated Fixation Letters, ap- 
pearing to the left of the mirror, are invalu- 
able in the Dynamic System of Skiascopy. 

"They are clearly cut in white against a 
black background, and being located in close 
proximity to the mirror, the refraction can- 
be estimated almost at the macula. These 
letters are rendered visible in the dark room 
by a divergent shaft of light which passes 
through an opening in the tube containing 
the lamp, which illuminates the mirror. This de zeng electric 
coincident illumination of the mirror and retinoscope. 



38 



SOURCES OF ILLUMINATION 



fixation letters obviates the necessity of any extraneous light, 
thereby affording the operator the advantage of a perfectly 
darkened room when so desired." 

The lamp used is of only one or two-candle power and is 
located behind, and close to, a strong convex lens, which serves 
to parallel the light radiation and thereby avoid any waste due 
to this cause, but like other electric lamps it, too, is sensitive to 
abuse. 

The light it gives is a fairly intense one and enables good 
work to be accomplished by those who are acquainted with its 

Fig. io. 




THE HARDY WALL BRACKET FOR GAS OR ELECTRIC LAMP. 



peculiarities. For dynamic work its fixation letters are limited 
in both numbers and position. 

As a portable light it is compact and easy of transportation 
and, in an emergency, serves the purpose of being useful as an 
ophthalmoscope as well. 

A point to bear in mind in connection with adequate illumin- 
ation in skiametric work is to have whatever lamp may be used 
so arranged that its adjustments, forward and backward to and 
from an examiner's own eye, are readily obtainable. The adjust- 
ment as to height is not so important as long as the light is 



VARIOUS SKIASCOPES 39 

about level with the patient's head and is situated from six to 
twelve inches to the patient's right. The alterable distance for- 
ward and backward is, however, quite essential, as it enables 
the intensity of illumination to be controlled by an examiner as 
his case demands. A very simple way to arrange for this is to 
use a wall bracket similar to the one shown in Fig. 10. 

This bracket is arranged for gas and electricity, and thus 
gives an examiner a double system of illumination which, in 
case of necessity, may prove of very great value in preventing a 
break-down. 

In summing up the question of illumination, perhaps the 
expression from the pen of a western specialist will serve to 
state the case fairly well. He wrote, rf I fully realize that 
proper illumination is the foundation of success in skiametry." 
And it may be added that this opinion is shared by many 
others who have had experience. 

VARIOUS SKIASCOPES. The confusion following the 
use of two forms of skiascopes, such as those having plane and 
those having concave mirrors, has led to the virtual abandon- 
ment of the latter by most of the skiametrists of the country. 
There are possibly some conditions under which a concave re- 
flector might give an examiner better service than a plane 
one would, but these are rare, and for general all-round skia- 
metric purposes the plane mirror is to be greatly preferred. All 
mirrors should be as brilliantly silvered as possible, and the 
reflections from them ought to be perfectly round and free from 
distortion. 

Regarding the size or working part of a mirror, this can be 
easily determined by holding it at the maximum distance at 
which it is to be used and covering its periphery with washer- 
like pieces of paper. The size of the reflecting surface neces- 
sary to produce the best results while in actual service can then 



40 VARIOUS SKIASCOPES 

be noted. This will usually be found to represent an area of 
about three-quarters of an inch in diameter. 

The central aperture, or peep-hole, should be as small as 
possible and yet permit of acute vision on the part of the 
examiner. A diameter of one or two millimeters is generally 
sufficient for the purpose. Having the handle at least six inches 
long will be found especially advantageous in using body move- 
ments. 

Keeping the peep-hole free from dust and dirt is also im- 
portant. A frequent twist of the skiascope just before it is 
used, and while its front and back are covered with a handker- 

Fig. II. 




A SIMPLE SKIASCOPE. 

chief held between the thumb and forefinger of the operator's 
hand, is usually all that is necessary in order to keep it quite 
clean. 

Fig. ii represents the skiascope generally employed in the 
practice of what is usually called "retinoscopy," where accom- 
modation is supposed to be relaxed by having the patient look 
over the examiner's shoulder, or where "a reliable cycloplegic" 
has been used. 

As will be seen in subsequent chapters, the use of cards for 
fixing the vision of the patient at the same distance away as that 



VARIOUS SKIASCOPES 



41 



at which the mirror is operated renders some means for attach- 
ing cards to the skiascope almost a necessity. Fig. 12 shows a 
device to which the name "Double Bracket Skiascope" has been 

Fig. 12. 




AUTHOR S DOUBLE BRACKET SKIASCOPE. 



given. The lenses in the disc at the back of this skiascope 
contain plus spherics of 1. D. 1.50 D. 2. D. 2.50 D. 3.D. 4.D. and 
5. D. for the purpose of correcting any presbyopia that an 



42 VARIOUS SKIASCOPES 

optometrist may have, himself, while working at any distance 
less than forty inches, so as to obtain a clear view of the action 
of the shadow. When an .examiner is under forty-five years 
of age the use of this lens disc is seldom required. 

The arrangement of the brackets attached to the mirror 
frame are such that the cards can be given a number of adjust- 
ments to suit possible contingencies. Also for the purpose of 
maintaining fixation so it can be relied upon, for variation in 
fixation means, of course, an alteration in the patient's refrac- 
tion. The usual procedure is for the examiner to request that 
the irregularly placed letters on the fixation card, Fig. 13, be 

Fig. 13. Fig. 14. 





SKIAMETRIC FIXATION CARDS. 

counted by the patient. Then, if this does not prolong the fixa- 
tion period sufficiently, the request is made to state what letters 
of the alphabet are missing, or what letters appear more than 
once. 

If the visual angle needs changing, or the focal fixation re- 
quires slight alteration, then the other fixation card, Fig. 14, 
can be made use of, reliable fixation being maintained by dis- 
puting the patient's count of the dots. The position of the Fig. 
13 card also has an advantage in its being placed so as to corre- 
spond with the examiner's own nodal point. When the light 
source is found unpleasant to the unused eye of an examiner it 
may be obviated by having card, Fig. 14, made longer and 
adjusted so as to act as a screen. 



HANDLING THE PLANE SKIASCOPE 43 

HANDLING THE PLANE SKIASCOPE. Regarding 
the proper way to handle a skiascope, the various tutors in 
skiametry differ, but all agree that the movements of the 
mirror should be of the slow, steady, straight-line order, and 
as free from wabbling and semi-circular motions as possible. 
When movements of the mirror are attempted by the hand- 



Fig. 


15. 






B 


Jsy HH 


1 m* i£ 


X*M 


m Wr 




w 


H$ m 










m Wr' 













MANNER OF HOLDING AUTHOR S SKIASCOPE. 

tilting method it takes many years of practice before a positive 
straight-line motion in all meridians of an eye can be depended 
upon. But where the movements are made by a body-tilting 
method the mastery of the mirror is very rapid, some beginners 
acquiring it almost perfectly after only a few days of practice. 
A description of this body method is as follows : The mirror 
handle is to be grasped near its lower end, when the skiascope is 



44 HANDLING THE PLANE SKIASCOPE 

held in a vertical position. The elbow and arm of the hand 
holding the mirror are to be pressed tightly against the side of 
the body, while the upper and inner edge of the metal disc, 
upon which the mirror is mounted, is to be held firmly against 
the side of the examiner's nose or resting on the eyebrow in 
such a manner that the peep-hole of the mirror is exactly in 
front of the operator's pupil. With the mirror handle held in a 
rigid manner, almost the entire body is made to assist in giving 
the proper movements. The examiner's upper torso, or trunk, 
acts as though it was pivoted at the waist, while the neck and 
heaving chest aid in the necessary motions. To say that this 
action involves a sort of courtesy, or bowing movement, might 
perhaps add to its description. Fig. 15 may also serve to give a 
better idea of how the skiascope should be held. 

It is always better for an examiner to learn to work with 
both eyes open when locating the reflected light on the face of 
a patient. After this location, the eye not in use at the peep-hole 
should be closed, so as to stimulate concentration and sharpen 
the brightness of the fundus reflex, as well as to define the 
shadow's edge. The closing of the unused eye serves to obviate 
any discomfort an examiner may experience, caused by the 
glaring light from the lamp in use, and especially so if the latter 
is at close range. 

The mirror light on the patient's face ought not to move 
over an inch in any one direction, and the pink pupil should 
hardly ever be allowed to pass entirely from view after once 
being found. The examiner should direct his attention to one 
edge of the patient's pupil only, as in this way he can quickly 
determine whether the shadow is with or against the mirror's 
movement in any one meridian. All movements should also be 
made very slowly, since rapidity of motion often interferes with 
judgment as to the shadow's action, just as the spokes in a 
wheel are found to be more difficult to count when the wheel 
revolves rapidly than when it goes slowly. 



NOVEL SKIASCOPES 45 

NOVEL SKIASCOPES. Among the novel devices for 
shadow seeing can be mentioned the Reisner "Retinoscope," 
shown in Fig. 16. 

The claims for this instrument are set forth by the manu- 
facturers as follows : 

Fig. 16. 




REISNER S RETINOSCOPE. 

"The Reisner Retinoscope has a small lever for tilting the 
mirror mechanically with self-recording axis on back. Tilting 
a mirror mechanically instead of the old way gives a positive 
movement straight across the meridian being neutralized, 
thereby avoiding the circular motion common with the ordinary 
mirror, enabling an operator to determine definitely the differ- 
ence between a case of conical cornea and mixed or irregular 
astigmatism. Referring to the back of the instrument, the 



46 NOVEL SKIASCOPES 

number indicated by pointer represents the axis at which lens 
should be placed in frame." 

Another departure in retinoscopes is the Klein "Non-Irritat- 
ing Retinoscope," shown in Fig. 17. 

The mirror of this instrument is made of amber glass sil- 
vered and mounted in the usual way. The makers ask the fol- 
lowing pertinent question : 

Fig. 17. 




KLEIN S RETINOSCOPE. 

"Why continue to use the ordinary white glass retinoscope, 
and cause needless annoyance to your patients, when, for a 
little more, you can obtain Klein's Non-Irritating amber glass 
retinoscope? This instrument is monochromatic, reduces the 
actinic rays, insures from ten to twenty per cent, greater dila- 
tion of the pupil and minimizes the diffused rays, which are 
annoying in the reflex of many eyes." 



CHAPTER III. 

Schematic Eye Practice and Its Importance to Students. 
— Model Eyes and the Exercise of Care in Their 
Adjustment. — Reduction and Transposition of Lens 
Values,, and the Necessity for the Complete Mas- 
tery of This Work in Successful Skiametry. 

SCHEMATIC EYE PRACTICE. Skill is called "famil- 
iarity with and dexterity in the execution of any science, art or 
handicraft," and no division of optometry calls for more prac- 
tice work, in order to be skillful, than does skiametry. 

It is exceedingly tiresome to a patient to sit quietly and 
have some inexperienced student gaze for minutes through the 
peep-hole of a mirror because he is unable to correctly determine 
the shadow's action. But with an experienced examiner it is 
different, all he needs is one or two flashes, or excursions of 
the reflected light, and the behavior of the shadow, under usual 
conditions, is made plain. 

Skill in this work can only come through experience, and 
experience gained through the use of a metal or paste-board 
model eye is just as valuable to the student as though it was 
gained through looking into a living organ of vision. 

Students can begin with large ocular pupils, and then, as 
their skill increases, these pupils can be made smaller and 
smaller. The expert in any field where skill is a factor is the 
one who practises morning, noon and night, or at every oppor- 
tunity that presents itself. 

Human eyes, owing to variations in the pigmentation of 
the fundus and to the uneven thickness of the corneal tissue 
giving rise to what is called "irregular" astigmia, are factors 



4 8 



SCHEMATIC EYE PRACTICE 



that make some living eyes most difficult to measure by means 
of the shadow test, so if an examiner makes himself a thorough 
master of the model eye, where conditions can be made ideal, 
he will have far less trouble with living eyes than if this pre- 
liminary practice on the model eye has been neglected. 

Fig. 18. 




THE DE ZENG-STANDARD SCHEMATIC EYE. 

SCHEMATIC EYES. For research work, as well as for 
practise, a good schematic eye requires careful selection and 
adjustment. The metal and pasteboard models that are on sale 
in all first-class optical supply houses offer a most excellent 
means for beginners to familiarize themselves with the prin- 
ciples of both skiametry and opthtalmoscopy. These eyes, how- 
ever, are frequently imperfect in construction, and the printed 



SCHEMATIC EYES 49 

scales attached to them are often unreliable. As a consequence, 
the student is apt to meet with discouraging results in his initial 
efforts to use them. Fig. 18 shows one of the newer makes of 
the all-metal kind, which has five sizes of pupil. 

The backs of these eyes are arranged for the insertion of 
colored miniature plates, which serve to illustrate the various 
pathologic conditions of the retina, and are to be used in con- 
nection with the study of ophthalmoscopy and the use of the 
ophthalmoscope. The double cell in front of the model eye 
makes it of excellent service in skiametric practice; as the well 

Fig. 19. 




QUEEN S PASTEBOARD SCHEMATIC EYE. 

marked axis scale also aids a beginner in obtaining the merid- 
ional accuracy which is so necessary to good work. 

The cheap pasteboard model, such as shown in Fig. 19, is 
usually found to be almost as trustworthy as the more expen- 
sive ones, but all of them require testing before their findings 
can be implicitly relied upon. 

A good way to determine the accuracy of these models for 
skiametric purposes is to have an experienced skiametrist put 
them to actual test by first setting the scale at "o," and then, if 
a one-diopter convex spherical lens causes a reversal of the 
shadow in all meridians at exactly forty inches away, it is quite 



50 SCHEMATIC EYES 

safe to rely on other findings made by means of the same model. 
To prove, however, that the scales are properly spaced it is wise 
to first test a few of the numbers on each side of the "o" before 
depending upon them for accuracy, for in optometric work in 
general it is so easy to be wrong and so difficult to be precisely 
right. 

All kinds of ordinary errors of refraction can be artificially 
created by means of these model eyes together with a few trial 
lenses. For instance, if an examiner is operating at a distance 
of forty inches away, by setting the model so that it shows one 
diopter of myopia and then by adding a one-diopter concave 
cylindric lens, he can create an error of one diopter of hyperopic 
astigmia. A one-diopter convex cylinder can be used to produce 
myopic astigmia of equal amount. Setting the model to show 
two diopters of myopia and then using a one-diopter convex 
cylinder lens will create a compound error of minus one-diopter 
spheric combined with a minus one-diopter cylindric, due allow- 
ance of one diopter having been made for the working distance. 

With the model showing two diopters of hypermetropia, if 
a two-diopter concave cylindric lens be added, the exact com- 
pound quantity represented by this error would be plus two 
diopters of spheric combined with plus two diopters of cylindric. 
And to neutralize it skiametrically at a distance of forty inches 
away would require an added lens power equal to plus three 
diopters spheric combined with plus two diopters cylindric. The 
added diopter of plus spheric representing the false myopia, 
often called the "working quantity." 

To illustrate a mixed astigmatic condition the model can be 
set to show two diopters of myopia, and then by adding a minus 
two-diopter cylinder at axis 90 an error representing minus one- 
diopter cylinder axis 180 combined with a plus one-diopter 
cylinder axis 90 can be obtained, which would require 
the addition of this lens quantity, or its equivalent, to neutralize 
it by means of the one-meter shadow test. And it will be noted 



REDUCTION OF LENSES 5 1 

that at whatever axis the cylindric lens is set the axis of the 
artificial astigmia will be in the same meridian. Thus it will 
be seen that a schematic eye can be made a very useful and 
patient patient. 

REDUCTION OF LENSES. In practical examination- 
room work with the skiascopic mirror it frequently happens 
that a saving of time and trouble is effected by making a test 
right over the patient's own glasses ; this test resulting, perhaps, 
in the discovery that a compound-lens quantity needs to be 
either added to or subtracted from the lenses then in use. 
Upon neutralizing these glasses it is found that they, too, are 
of the so-called "compound" type, therefore an examiner must 
be possessed of knowledge that will enable him to tell the exact 
ray-bending power of the four lens quantities involved and to 
do it with ease and without waste of time or likelihood of mak- 
ing mistakes. Now while this subject is not classified as be- 
longing to theoretic skiametry, yet it is, nevertheless, a very im- 
portant factor in contributing toward successful shadow work, 
and especially so in connection with the dynamic method, for ski- 
ametry is sometimes considered as neutralization at long range. 
Therefore a few pages will here be given to what is thought 
to be a very simple solution of a so-called complex subject. 

In the consideration of most problems there is the unit or 
lowest appreciable quantity to be dealt with, so it is with lenses. 
Speaking microscopically the basis of all lenses can be said to be 
prisms, but speaking macroscopically, the unit of all lenses is a 
cylinder. Therefore, if it is learned how to combine these cylin- 
ders, after having reduced all lens quantities to a cylindric basis, 
the transposition of lenses will be found to be a very easy task, 
no matter whether the lens quantities dealt with number few or 
many. 

This principle is much like the one in the old story related 
of the quack doctor who had two bottles of medicine with 



52 



REDUCTION OF LENSES 



which he could cure all the ills that flesh was heir to. His plan 
was to give doses out of one bottle which turned every ailment 
into fits, then the remedy in the other bottle cured the fits, and 
the patient got well. 

To carry out a similar procedure it must be considered that 
two cylindric lenses of like kind and strength when crossing one 
another at right angles are equal to a spheric lens. Hence the 
reverse follows, that a spheric lens is equal to two cylindric 
lenses crossing one another at right angles, and whose kind and 
strength are the same. 

In the optometrist's consideration of cylinders he will never 
need them at any other than at right angles to one another, no 



Fig. 20. 



j-m 




+2.D. 



TWO CYLINDRIC LENSES OF UNEQUAL FOCUS AND AXIS. 



matter whether they are plus and plus or minus and minus, of 
the same or unequal strengths, or whether they are 
plus and minus or minus and plus, equal or unequal, etc., etc. 
Their axes will always be at right angles, and for the simple 
reason that if they were crossed at any other than right angles 
their combined refraction would show a sphero- cylindric effect, 
which could be duplicated by right-angle cylinders. 

Now, in a combination of cylindric lenses of unequal 
strength, but of the same kind, it will be seen that when their 
axes are at right angles to each other their combined refraction 
will be equal to that of a compound lens whose component parts 



REDUCTION OF LENSES 



53 



are of a like nature : as a plus one-diopter cylinder set at right 
angles to a plus two-diopter cylinder is equal to a plus one- 
diopter spheric combined with a plus one-diopter cylindric. The 
second cylinder in the above case having been robbed of a 
quantity equal to the strength of the first cylinder, in order to 




■t-ZD 



A CROSSED-CYLINDER LENS OF UNEQUAL MERIDIONAL FOCUS'.. 



convert the first one into a spheric quantity. The robbery is 
noted and due allowance made therefor. 

By referring to Fig. 20 it will be seen that the cylinder lens 
"a" has a ray bending power of plus 1. D., while cylinder lens 



Fig. 22. 



+UL 



HD 



THREE CYLINDRIC LENSES OF EQUAL FOCUS. 
AND TWO AT AXIS l8o. 





HD 



ONE AT AXIS 90 



"b" has a power of plus 2. D. Their axes, of course, are at 
right angles to each other, also to their ray bending power. If 
these two lenses were merged back to back their appearance 
would be illustrated by Fig. 21. 



54 



REDUCTION OF LENSES 



Instead of two cylinders being used, one plus I. D. and the 
other plus 2. D., it is shown in Fig. 22 that three plus 1. D. cylin- 
ders can be employed to accomplish the same purpose as those 
in Fig. 20. 

In Fig. 23 it is shown that lens "a" has been converted 
into a 1. D. spheric quantity by the use of the borrowed lens 
"c" of Fig. 22, and as it takes "c" and "d" to equal the plus 
2. D. of "b" in Fig. 20 it is plain that "d" is the remaining 
quantity. Thus the formula: 

+ 1. D. C. axis 90 C + 2. D. C. axis 180 equals + 1. D. S. 
C + 1. D. C. axis 180. 

Fig. 23. 





ONE CROSSED-CYLINDER OF EQUAL MERIDIONAL FOCUS AND ONE 
SIMPLE CYLINDER AT AXIS l8o. 



Except for purposes of analysis, the crossed cylinder is 
never to be generally employed, he who prescribes it other- 
wise only exhibits his ignorance of lenses and their uses, as 
the function of a lens is to bend rays of light, and it matters 
little whether this bending is done by two cylinders crossing 
one another at right angles or whether it is accomplished by 
means of a lens where one surface has a spheric curvature. 
This rule also applies to "toric" lenses where the curves of one 
surface of revolution are ellipsoidal in character, made so by 
having one meridian of curvature either greater or less than 
the one at right angles to it. 



REDUCTION OF LENSES 55 

To crowd an examiner's head with arbitrary rules is likely 
to lead to confusion, so that in the case of transposing lenses 
it is well to simplify the process as much as possible. There- 
fore, in imitating the method of the quack doctor with his two 
medicines, it will be necessary to first reduce all lens quantities 
to a cylindric basis and then commit to memory two short rules 
for the transposition of cylinders. The following extra long 
combination may, perhaps, serve to make this reduction 
principle plainer: 

+ i. D. S. C + 2. D. C. 90 3 — ■ 1. D. C. 180 C + 1. D. 
S. C — 2. D. C. 90 C — 2. D. S. 

Here, it is seen, there are six lens quantities whose chief 
axes are 90 and 180 degrees. After creating two columns, all 
of the lens quantities are written in their cylindric equivalents 
whose axes come under these two headings, not forgetting that 
each spheric lens is to be written twice as it is equal to two 
crossed cylindric ones whose strength and kind are the same. 
The following is then obtained : 

Axis 90 Axis 180 

+ 1. + 1. 

+ 2. — 1. 

+ 1. + 1. 

— 2. — 2. 

— 2. 



o 

In the axis 90 column the totals are -f- 4. D. and — 4. D., 
which, of course, neutralize one another. In the axis 180 
column the totals of — 3. D. and -f- 2. D. leave a remainder 
of — 1. D. axis 180. 

Take this example for instance: 

+ 0.50 D. C. 45 C + 0.25 D. S. C + 0.2s D. C. 135. 



56 REDUCTION OF LENSES 

Here the two chief axes are 45 and 135 degrees, and pro- 
ceeding as before the results are : 

Axis 45 Axis 135 

+ 0.50 + 0.25 

+ 0.25 + 0.25 



+ 0.75 + 0.50 

The totals give one cylinder of + 0.75 axis 45 to be crossed 
by another cylinder of -f- 0.50 D. axis 135, the symbols being 
alike. 

Now another example in reduction: 

+ 1.25 D. S. C — 1.75 D. C. 15 C — 0.75 D. S. 
C — 0.25 D. C. 105. 

Being reduced, the results obtained are : 

Axis 15 Axis 105 

+ 1-25 + 1-25 

— i-75 — o-75 

— 0.75 — 0.25 



— 1.25 + 0.25 

This gives a total of one cylinder of — 1.25 D. axis 15 being 
crossed by another cylinder of -j- 0.25 D. axis 105, the symbols 
being unlike. 

In the three examples shown all lens quantities have been 
converted into cylindric equivalents, so that in order to master 
them the two short rules before mentioned must be used for 
the transposition of these cylinders, and then the simple les- 
son will have been acquired. 

TRANSPOSITION OF LENSES. Rule No. i.—In a 
combination of cylindric lenses of a like character, such as plus 



TRANSPOSITION OF LENSES 



57 



and plus, or minus and minus, the strength of the weakest 
cylinder should be written as the spheric quantity while the 
difference between the two lenses should be written as a new 
cylindric quantity, the axis of the stronger cylinder governing 
the axis of the cylinder in combination, thus: 

+ 0.75 D. C. axis 45 C + 0-50 D. C. axis 135 should be 
written as equal to -f- 0.50 D. S. C + 0.25 D. C. axis 45. 

Rule No. 2. — In a combination of cylindric lenses of dif- 
ferent character, such as plus and minus, or minus and plus, 
the strength of either cylinder can be written as a spheric quan- 
tity while the (arithmetical) sum of the two cylinders should 




_ 125 D. 



crossed-cylindric lens of plus and minus curvatures. 



be written as a new cylindric quantity, the axis of the second 
lens governing the axis of the cylinder in combination, thus: 

— 1.25 D. C. axis 15 C + 0-25 D. C. axis 105, 

can be written in two ways, the better way being to write it 
with the minus quantity first, so as to obtain a periscopic effect 
in the completed lens, this produces : 

— 1.25 D. S. C + i-50 D. C. axis 105. 

Or an equal refractive quantity can be obtained by writing 
it in this way: 

+ 0.25 D. S. C — i-5o D. C. axis 15. 

Fig. 24 shows a plus 0.25 D. C. lens "a" at axis 90, being 



58 



TRANSPOSITION OF LENSES 



crossed at right angles by a minus 1.25 D. C. lens "b." Fig. 25 
shows that the plus 0.25 D. cylinder "a" must be crossed by a 
plus 0.25 D. cylinder "c" in order to convert the "a" lens into 
a spheric quantity, and that the "b" cylinder must then be in- 
creased to minus 1.50 D. in order to produce a ray bending 
power of minus 1.25 D. after the strength of the borrowed lens 
"c" has been neutralized. 



Fig. 2q. 




t-SDB 



THREE CYLINDRIC LENSES, TWO PLUS AND ONE MINUS. 



It will be noted in Rule No. 2 that the word " 'arithmetical" 
is parenthesized, this is done to indicate that for purposes of 
common understanding liberties have been taken with an 
algebraic problem. 

To re-transpose any of these combinations it is only neces- 
sary to proceed by the usual reduction to cylindric form and 
then apply whichever one of the two simple rules that may be 
called for. 

There is one other form of transposition which it might be 
well to mention here, and that is in the changing of plus and 
plus and minus and minus compounds into plus and minus or 
minus and plus equivalents for the purpose of producing 
meniscus forms of lenses. For instance, the following two 
formulas "a" and "b" have like ray bending powers, also "c" 
and "d." 



TRANSPOSITION OF LENSES 59 



a. 


+ 1. 


D. 


S. 


C + 1. 


D. 


C. 


axis 90, 


or 


b. 


+ 2. 


D. 


s. 


and 


D. 


C. 


axis 180 




c. 


— 1. 


D. 


s. 


C — i- 


D. 


C. 


axis 180, 


or 


d. 


— 2. 


D. 


s. 


C + 1. 


D. 


C. 


axis 90. 





The rule governing this transposition is as follows; 

Rule No. 3. — Add the two lens quantities together for a 
new sphere, change the symbol of the cylinder and alter its 
axis ninety degrees. 

The world, metaphorically speaking, takes off its hat to 
the mathematician, so if the optometrist desires that deference 
be shown him, too, he must acquire enough of mathematics to 
make himself proficient in his work. 

Procrastination and the plea of "no time to take up higher 
optics" will neither advance the individual nor the profession 
to which he belongs. Self-education is just as good as any- 
other kind, provided it accomplishes its object; therefore let 
him who desires to make substantial skiametric advancement 
remember that the greatest service he can do himself is to 
thoroughly master the rudiments of light and lenses and to 
acquire the ability to juggle with all kinds and quantities of 
ray and lens values. 



CHAPTER IV. 

Why Ocular Pupils Appear Red When Viewed Through 
a Skiascope With a Brief Description of the Card- 
inal Points Involved in Static Skiametry, as Prac- 
tised with the Plane Mirror, Including Some 
Theories Regarding Fundus Reflex. 

WHY PUPILS APPEAR RED. Before considering 

•retinal illumination it will be well to again call attention to 
the fact that all visible objects that do not generate light must, 
of course, reflect it, hence every non-luminous object that can 
be seen may be considered as being some kind of a mirror'. 
Glass with amalgam backing, as before stated, makes the best 
reflector, while a dark uneven surface, like black velvet, makes 
the poorest. With a so-called "looking glass" the rays of light 
are reflected in an almost unbroken manner, whereas with most 
visible objects their surfaces are such as to break up the light 
into irregular rays, or angles of reflection. This breaking up 
being well illustrated by a lamp having a clear glass chimney, 
and one whose chimney is of the ground or "frosted" kind. In 
the clear glass the flame is the true source of light. In the 
ground glass the surface of the chimney is the apparent source. 
The inner back part or, so-called, fundus of an eye is about 
the same sort of a mirror as rough red tissue paper makes, and 
as it is necessary to illuminate this fundus in order to obtain an 
apparent source of light, or target, from which to measure 
emergent rays, it will be seen that consideration of why the 
pupil of an eye appears red through the peep-hole of a skia- 
scope will be well for all students to understand, reference is 
therefore to be had to Figs. 26, 27 and 28. 



WHY PUPILS APPEAR RED 



6l 



In Fig. 26 the candle "a" radiates light rays which fall on 
card "b" and pass through the aperture "c" thus illuminating a 
portion of card "d." 

Fig. 26. 




d a 

ILLUMINATION OF SECOND CARD THROUGH HOLE IN FIRST ONE. 



Card "d" being something of a mirror, reflects the light from 
the illuminated spot, or area, "e" in all directions, some of 
which, of course, passes back again through the aperture "c" 
in card "b," as shown in Fig. 27. An eye, therefore, at "f" in 

Fig. 27. 




RETURN RAYS FROM SECOND CARD ENTERING EYE THROUGH TUBE 

IN CANDLE. 



order to see the edge, or any portion, of the illuminated area 
"e" on card "d," must be placed behind a tube "h," which passes 
through the flame of the candle "a," where it will then be en- 
abled to intercept the returning rays from "e." 



62 



WHY PUPILS APPEAR RED 



In Fig. 28, the skiascope "g," having a peep-hole in the 
center of its mirror, practically replaces the tube "k," shown in 
candle "a," of Fig. 27. The eye "f" in Fig. 28 is therefore 
enabled to see the illuminated area "e" on card "d." Now, by 
enclosing cards "b" and "d" in the rim of a hollow sphere and 
placing a lens over the aperture "c" in card "b," there would be 

Fig. 28. 




SUBSTITUTING A SKIASCOPE FOR CANDLE TUBE. 



created the optical principles of a real eye whose pupil would 
appear red, because the fundus of the eye would be visible to 
an observer. This observer could then readily see the posterior 
inner surface of the eye where the mesh work of blood vessels 
gives it the usual pink-like appearance so familiar to the expe- 
rienced examiner. It follows, therefore, that the reason why 
the pupil of an eye ordinarily appears black is because returning 
rays can not be intercepted without using an instrument. 



RETINAL ILLUMINATION 6$ 

RETINAL ILLUMINATION. Subjective optometry can 
be said to be the treating, or bending, of rays of light before 
they enter an eye, whereas, objective optometry can be called the 
bending of the rays after they leave the eye. 

Rays entering an eye can be of two kinds, those that proceed 
direct from some light source, such as a lamp flame, and those 
that are reflected from some kind of a mirror. In either case 
the fundus of -the eye is illuminated, and the intensity of the 
illumination is dependent upon the distance that the rays have 
traveled, and to the quality of the mirror that reflects them. 

Rays traveling in the form of a beam of light can be made 
to enter the eye parallel, convergent or divergent, and the size 
of the retinal illumination is dependent upon this parallelism, 
convergency or divergency. 

Retinal illumination is a necessity in skiametry,, because 
some kind of a target, or apparent light source, must be ob- 
tained from which the emergent rays can emanate, and the 
means for obtaining this target is to be had by reflecting light 
from a lamp flame into a patient's eye, and then by intercepting 
the returning or reflected rays, at the peep-hole of a skiascope, 
an examiner is in a position to measure these rays and thus to 
determine the state of the patient's refraction. 

Two factors in skiametric work must be kept in mind, namely, 
that the entering rays are solely for the purpose of creating a 
source from which the emerging rays can start, while it is the 
angle of the emerging rays, alone, which denotes the refractive 
condition of the eye, and it is the measurement of these emergent 
rays that gives the name of shadow measuring to skiametry. 
The so-called "shadow" being created by the inner edge of the 
iris, which limits the size of the illuminated area on the retina, 
made by the entering rays of light. 

Errors of refraction, and the distance from the external 
light source, serve to influence the size of the retinal light spot, 
and this, in turn, influences the speed and brightness of the 



64 



RETINAL ILLUMINATION 



shadow in its skiascopic behavior, but it has no direct bearing 
upon the refraction of the eye under measurement, as the 
emergent rays originate from the internal light source created 
by the illumination on the retina, and it is the movement of the 
edge of this light spot that gives the with and against motions 
of the shadow, made mention of later on. 

In Fig. 29, "a" is the external light source, "b" is the skia- 
scope, "c" the lens system of the eye, "d" the retinal illumina- 
tion, or light spot, and "i" the focus of the entering rays, which 
the retina stops at "d." 

Fig. 29. 




ILLUMINATING THE OCULAR FUNDUS. 



The size of "d," it will be easily seen, is regulated by the 
positions of "a" and "b," for if the light source, or the mirror, 
is near to the eye then "d" will be larger than if either one were 
farther away. 

Fig. 30 shows the fundus of an eye with an illuminated area 
of light, "e" the shadow being represented by "d, d, d, d," while 
"g" calls attention to the demarcation between "d, d, d, d," and 



SHADOW PHENOMENA 65 

"e." This demarcation creating the edge of a target, or curved 
line of light, acting as a source from which measurements can 
be calculated. 

Fig. 30. 




THE ILLUMINATED AREA ON THE FUNDUS. 

SHADOW PHENOMENA. In Fig. 31 the marginal line 
g," between the light spot "e" and the non-illuminated area 
d" "d" constitutes the starting point for the emerging rays, and 

Fig. 31. 



e~. 




RAYS RETURNING FROM EDGE OF ILLUMINATED AREA ON THE 

FUNDUS. 

if the lens system "c" is in proper relation to the target "g," 
producing what is known as emmctropia, the rays will emerge 

parallel. 



66 SHADOW PHENOMENA 

On the other hand, if the emerging rays diverge or converge 
in one or more meridians of the eye it denotes an error of re- 
fraction of some kind. 

When a convex lens of known power is placed in front of an 
emmetropic eye, as shown by "k" in Fig. 32, the emerging 
parallel rays will be brought to a focus, or crossing point, at the 
focal length of the lens used, and if at this focal point an exam- 
iner places his own eye behind the peep-hole of a skiascope, at 
"h," he will be unable to note any motion of "g," or of any 
appearance of a shadow in the pupil of the patient's eye. On 
the contrary, if he advances toward the patient so that the 
point of crossing of the emergent rays is behind his own eye, 



Fig. 32. 




g V y k h 

RETURNING RAYS INFLUENCED BY A CONVEX LENS. 

then he can note, if he is skillful, that "g" now appears as the 
edge of a pupillary shadow and moves with the movement of 
the light on the patient's face as he rotates his skiascopic mirror 
from side to side or top to bottom across the eye. And if the 
eye is emmetropic this movement of the shadow will be alike in 
all meridians of rotation. 

The reverse order prevails if the examiner recedes from his 
patient, so that the focus, or crossing point of the emergent rays, 
is in front of his own eye, then all rotations of his skiascopic 
mirror cause the shadow to move against the light that is re- 
flected on the patient's face. This crossing point off the 
emergent rays then becomes known as the "point of reversal" 
of the shadow, and this reversal point enables an examiner to 



THE SHADOW'S ACTION 6j 

determine the refractive status of his patient's eye, either by 
altering the distance of his view-point, or by changing the 
strength of lens "k" so the rays will focus, or cross, at any 
given point selected. The difference between the lens an eye 
ought to take to produce the shadow's action at a given point, 
and the lens it actually does take, constitutes the measurement 
of the error. 

THE SHADOW'S ACTION. Just why the shadow be- 
haves in the with and against manner here described can be 
seen by reference to Figs. 33 and 34. 

In Fig. 33, if a single ray is followed from the point of the 

Fig. 33. 





Ptifierife eye £xaminerh eye 

WHY THE SHADOW MOVES "WITH" THE MIRROR. 

arrow, "e," on the fundus of the patient's eye, to "e"' on the 
fundus of the examiner's eye, the two arrows will be seen to 
point in the same downward direction. All motion can then 
be said to be synchronous, or coincident, as the upper emergent 
ray from the patient's eye becomes the upper entering ray of 
the examiner's eye. 

In Fig. 34, owing to the refraction by lens "k," the upper 
emergent ray from the arrow's point "e" in the patient's eye be- 
comes the lower entering ray of the examiner's eye, and the 
arrow "e" undergoes a reversal of position at "e"' by pointing 
upward. Motion can then be said to be opposite, or against the 
skiascopic movement of the facial light. 



05 THE SHADOW S ACTION 

It is this motion of the shadow with and against the skia- 
scope^ movement that enables an examiner to locate the cross- 
ing "x" of the emergent rays, and the distance from the patient's 
eye at which this crossing occurs, together with the lenses neces- 
sary to cause it, constitute the means for determining the meas- 
urement of the error. Thus if a plus 1.50 D. lens, "k," is 
required to create a crossing of the rays at forty inches from an 
emmetropic eye, whose accommodation is relaxed, then the 
error would be plus 0.50 D., because plus 1. D. is the correct 
strength for a lens necessary to cause a crossing at this distance. 

If a lens of only plus 0.25 D. caused a crossing of the rays at 
forty inches from the patient's eye, then the error would be 

Fig. 34. 

Patients eye x Examiners eye 

WHY THE SHADOW MOVES "AGAINST"" THE MIRROR. 

minus 0.75 D. And if twenty inches was the distance selected 
for the crossing, then plus 2. D. would be the working lens "k," 
from which calculations should be made, instead of plus 1. D. 
Skiametry has been ably described by Burnett as being con- 
trolled by the law of conjugate foci, therefore if an emmetropic 
or hyperopic eye is made artificially myopic, the strength of the 
lens required to produce this artificial myopia must enter into 
the final calculations. And if, on the other hand, the eye has 
true myopia, then the amount of the error can be easily deter- 
mined by finding the crossing point of the emerging rays. Thus 
if the rays crossed at fifty-three inches from the patient's eye 
the error would be neutralized by a lens of minus 0.75 D If 



THE SHADOW'S IMITATION 69 

the crossing was at twenty-two inches distance, then the lenses 
needed would be minus 1.75 D. 

THE SHADOW'S IMITATION. Fig. 35 will convey a 
slight idea of the appearance of a so-called "shadow" in passing 
across the pupil of an eye. 

A much better illustration of this shadow phenomenon can be 
had by taking a piece of cardboard, say six inches square, and 
cutting a hole in it one inch in diameter, then by pasting over 
this aperture a piece of pink, translucent paper, and by holding 
the card before a lamp, a fair idea of the reddish appearance of 
the pupil of an eye when looked at through a skiascope may be 

Fig. 35. 




PUPILLARY APPEARANCE OF A SO-CALLED SHADOW. 

had. The edge of another piece of cardboard passed between 
the first card and the lamp will, by varying the distance, give a 
very good representation of the shadow as seen in an eye by 
means of a skiascope. 

SHADOW MEASURING. All eyes must be measured in 
two or more meridians, so as to determine the greatest and 
least refraction. If these two are vertical and horizontal, and a 
plus 1. D. S. is placed before a patient's eye and the shadow is 
found to reverse at forty inches in the horizontal meridian, and 
at twenty inches in the vertical, then the error could be neu- 
tralized by a lens of minus 1. D. C. axis 180, but if it took 
plus 1. D. in the vertical and plus 2. D. in the horizontal, then 



JO SHADOW MEASURING 

the lens required would be plus i. D. C. axis 90. Or if it took 
plus 2. D. in the vertical and plus 3. D. in the horizontal, then 
plus 1. D. S. combined with plus 1. D. C. 90 would be the lens 
indicated. 

It will be noted that 1. D. of artificial myopia was first 
created for the forty inches observation point, then in the final 
deductions this created myopia was allowed for. 

If true myopia was present then no artificial myopia would 
be needed, unless the true was weaker, and had a point of 
crossing farther away than the point of observation. To illus- 
trate this, suppose the true myopia was a half-diopter, the 
emergent rays would then cross at eighty inches, and if forty 
inches was selected as the point of observation the crossing of 
the rays would occur back of the examiner's skiascope, and the 
motion of the shadow would be with the mirror, the same as in 
emmetropia without lenses. In emmetropic, however, the plac- 
ing of a plus 1. D. lens before the patient's eye would cause 
crossing at forty inches, but in a true myopia of a half-diopter the 
plus 1. D. lens serves to overdo the matter, therefore, a plus 
0.50 D. would be the needed lens, or, if the observation was 
changed to twenty-six inches then the crossing could be found 
without changing the 1. D. lens. So the rule, before mentioned, 
that the difference between that which an eye does take and 
that which it ought to take, to cause reversal at a given point, 
represents the error of refraction in the meridian measured. 

PRACTICE OF STATIC SKIAMETRY. In the practical 
application of static skiametry, a fifty-candle power light source 
should be situated at the patient's right, on a level with, and 
from six to twelve inches from, his ear. After placing a trial 
frame before the patient's eyes, two plus 4. D. S. lenses are 
to be inserted in each cell of the frame and the patient directed 
to look over the examiner's shoulder at some object placed 
twenty or more feet away, the examiner to be seated squarely 



PRACTICE OF STATIC SKIAMETRY Jl 

in front of the patient and operating his piano skiascope exactly 
forty inches from the patient's eyes. In emmetropia, under these 
conditions, the shadow will move against the mirror in all 
meridians, and the four diopters of lens power will have to be 
reduced to one diopter before reversal, or the neutralizing point 
of the emerging rays, occurs, the plus one-diopter lens being 
the so-called "working quantity" for an examination that is 
made at forty inches. 

In hypermetropia of, say, one diopter the reduction of the 
four-diopter lens would be two diopters. And of these two 
diopters one diopter would represent the error, and the other the 
working quantity or artificial myopia necessary to create a 
standard condition, variations from which are to be measured 
by adding or subtracting lenses, or by altering the distances at 
which observations are made. This can be illustrated as fol- 
lows : In a true myopia of, say, two diopters the movement of 
the shadow would still be against the mirror, even after the four- 
diopter lens had been removed, the examiner could then add 
minus spheric lenses, or he could advance his skiascope up to 
within twenty inches of the patient's eyes, as the emergent rays 
from the retina of an eye having two diopters of true myopia 
would have a conjugate focus at this distance. 

Had the eye been myopic one diopter, the conjugate focus 
would have been exactly at forty inches without lenses of 
any kind, hence the rule in calculating all errors of 
refraction in static skiametry, where the working, or observation, 
distance is forty inches, is to add one diopter of minus quantity 
to the total findings, and this sum will then represent the error. 
Astigmia being truly a half -spherical error the examiner is to 
proceed as in simple hypermetropia or myopia, with the excep- 
tion that the error is to be measured only in the meridian at 
right angles to the axis, and the axis is to be determined by 
noting the meridian in which there is no motion of the shadow 
when the zvorking lens is in position. 



*]2 PRACTICE OF STATIC SKIAMETRY 

Take as an example a patient with two diopters of hyperopic 
astigmia in the horizontal meridian ; if the examiner operates at 
forty inches with a plus one-diopter spherical lens before the 
patient's eye he will note a marked movement with the mirror in 
the horizontal meridian, but no movement in the vertical, this 
being the meridian of no error it is of course the axis. So, after 
noting this axis, by the general band-like appearance of the 
shadow, and that the error at right angles to this axis is 
hyperopic, all that remains for the examiner to do is to de- 
termine how great the error really is, and this is ascertained 
by adding plus lenses until reversal occurs. 

Lenses used for neutralizing purposes can be either spheric 
or cylindric, for it will be remembered that two cylinders of 
equal strength and kind with their axes crossing one another at 
right angles are equal to a sphere. Therefore any astigmia where 
the axis is vertical can be measured by the aid of a spheric lens 
used in its horizontal meridian, the vertical meridian being ig- 
nored. Where cylindric lenses are used great care must be exer- 
cised in placing the axis of the cylinder so it exactly coincides 
with the astigmatic axis of the eye, otherwise confuson of 
shadow-action and inaccuracies will occur. 

So-called "compound" and "mixed" errors can be considered 
as being astigmatic in the two meridians of greatest and least 
refraction that are at right angles to each other. After a 
working lens is in position, suppose it takes a plus one-diopter to 
arrest the motion in the vertical meridian, and a plus two-diopter 
to do the same in the horizontal, then the case could be likened 
to a one-diopter cylinder being crossed by a two-diopter cylin- 
der, which, if transposed, would resolve itself into the following 
formula: plus I. D. S. combined with a plus I. D. C. axis 90. 

Looking at it another way, if the vertical meridian had taken 
a minus instead of a plus lens to neutralize its error the formula 
would then read minus 1. D. C. axis 180 crossed by a plus 
2. D. C. axis 90, or transposed it would equal a minus 1. D. S. 



THEORIES REGARDING DULL REFLEXES J$ 

combined with a plus 3. D. C. axis 90, so that all cases of com- 
pound and mixed errors are merely cases of crossed cylinders, 
and are capable of neutralization by either spheric or cylindric 
lenses. 

THEORIES REGARDING DULL REFLEXES. In 
the consideration of a subject as broad as the term ocular 
skiametry would indicate, the temptation of an author to soar 
his kite in the realm of speculation and attach to its tail a few 
theories of his own is very great indeed, even if some of the 
theories should prove "bad pennies" and return to embarrass 
their giver. 

In the actual practice of skiametry there arise certain little 
details which might be considered as sub-phenomena, and which 
exercise a more or less important bearing upon the system as a 
whole. Attention will therefore be invited to a few of these 
points which may perhaps savor more of theory than they do of 
practice but which, nevertheless, seem to answer natural ques- 
tions likely to arise in the mind of those who desire to know the 
why of everything they are interested in. 

Ocular pupils of a size not exceeding two millimeters in 
diameter, notwithstanding an examiner's ability to magnify 
them, are often very troublesome and constitute a part of the 
cases which it is wise to determine by means other than by 
skiametry. This is especially true if, in addition to the small- 
ness of the pupil, the fundus reflex is of the deeply pigmented 
or dull kind. The reason for this is due not so much to a failure 
on the part of the examiner to see the pupil as it is to the fact 
that the pupillary aperture prevents a sufficient volume of light 
from entering the eye in order to create a shadow sharp enough 
in outline to be readily measured. 

In expecting to occasionally find some dull ocular fundi 
the examiner must not mistake high degrees of myopia, nor 
hyperopia, for excessive pigmentation. Especially in myopia. 



74 



THEORIES REGARDING DULL REFLEXES 



even in an error of only four or six diopters, will the examiner 
sometimes be puzzled to determine why the reflex is so poor. 
Adding correcting glasses, however, often brightens this reflex 
in proportion as the correction nears the total, although at 
the exact reversal point of the shadow the reflex may again 
become very unsatisfactory, as may also the movements of the 
shadow at this time. 

A slow motion must not be mistaken for no motion. For 

Fig. 36. 




WHY THE RETINAL ILLUMINATION IS LARGER IN AMETROPIA 
THAN IN EMMETROPIA. 



if Fig. 36 is looked at it will be seen why pronounced degrees 
of either myopia or hyperopia make large light areas on the 
retina, thus requiring a longer time for the shadow surround- 
ing the light circles "b" and "c" to come into view than if 
these illuminated areas were smaller. 

Fig. 37 also shows this principle emphasized in a myopic 
eye, the returning rays from the edge "d" of the illuminated area 
"b" illustrating the distance the shadow must traverse before 
reaching the opposite side, this area being much larger than 



THEORIES REGARDING DULL REFLEXES J$ 

if the eye was an emmetropic one, where the proportion would 
be similar to "a" in Fig. 36. 

The fact that a reflex in a given error of myopia is much 
duller than in a corresponding one of hypermetropia is due, 
no doubt, to the greater distance the returning rays travel in 
a myopic eye than in an emmetropic or hyperopic one before 
reaching the pupillary opening which, consequently, diminishes 

Fig. 37. 



b- 



WHY SHADOWS MOVE SLOWER IN AMETROPIA THAN IN 
EMMETROPIA. 

their number through radiation and absorption. Fig. 38 illus- 
trates a theory for this. The lines "h' e' m'" show the relative 
loss by quenching as the divergent rays from a given illumina- 
tion on the retina of a myopic, emmetropic, or hyperopic eye 
strike the inside of the iris, which serves to diaphragm part of 
them and prevent their further egress. The hyperopic eye, 
owing to its shorter depth, permits of the least interference 
with its radiation, but its retinal illumination, see "c" in Fig. 
36, shows why its reflex is dull, though not as dull as that of 
the myopic eye "b," of Fig. 36. 

Fig. 39 shows the comparative loss in intensity of illumina- 



7 6 



THEORIES REGARDING DULL REFLEXES 



tion in eyes whose myopic or hyperopic error varies from one 
to sixteen diopters, "a" to "i" showing the relative size of the 
retinal area, illuminated, and thus accounting for the especially 
poor reflex in marked degrees of myopia. 

Brightness of reflex, however, is not all there is to skiam- 
etry, for, owing to the optical phenomena called "penumbra" 
it is sometimes possible to obtain a more defined shadow under 



Fig. 38. 




L 



e m 



WHY A SHADOW IS DULLER IN MYOPIA THAN IN A LIKE DEGREE 
OF HYPERMETROPIA. 



a moderate illumination than it is under one more intense. A 
reason for this is suggested in Fig. 40. But just what part 
the numerous penumbra play in interfering with the sharp- 
ness of demarcation of the shadow it is difficult to ascertain, 
for the emerging light casts its penumbra at the peep-hole 
of the examiner's mirror just as the entering light does at 
the pupil. And when it is considered that a round aperture 
is being dealt with it will be seen that the conditions are even 
more complex than would ordinarily manifest themselves if 
the shadow cast was a central one instead of being peripheral. 



THEORIES REGARDING DULL REFLEXES 



77 



Figs. 40 and 41 may serve to make this subject better under- 
stood for, as has been said before, a sharp shadow is a great 
aid to good work. 

Fig. 39. 




RELATIVE SIZE OF RETINAL ILLUMINATION IN HIGH AND LOW 
DEGREES OF MYOPIA. 



Fig. 40. 




THE OPTICAL PRINCIPLES OF PENUMBRA. 



In Fig. 41 the same principle can be seen as is shown in 
Fig. 40, only the conditions are doubled, for here there are 
three points on the candle flame instead of two, the central 
point acting in a manner which virtually makes it the same 
as though four points had been selected. The opaque object 



78 



THEORIES REGARDING DULL REFLEXES 



"a" interferes with the passage of the horizontal rays of light 
from the candle "c." The oblique rays, however, pass at dif- 
ferent angles and give rise to confused shadows as illustrated 
by "d 1 " and "dV 

In Fig. 42 this principle has been adapted to an eye where 
two points of illumination are again shown whose source is 
located on the mirror-like retina, for it is only the center of 
the shadow that is involved, this shadow being produced by 

Fig. 41. 




THE OPTICAL PRINCIPLES OF PENUMBRA DOUBLED. 



the iris acting as an opaque object. If either a plus or minus 
lens is placed in front of this eye it merely serves to refract 
all the light in accordance with the lens selected, the penumbra 
still remaining to add to the indistinctness of the edge of the 
shadow. 

If this phenomenon could be overcome it would, seemingly, 
contribute much toward that skiametric accuracy for which all 
skiametrists are striving but, as heretofore shown, if a gain be 
made in one direction a loss is quite sure to follow in another, 
so that examiners must be content with fuzzy shadows until 



THEORIES REGARDING DULL REFLEXES 79 

some one solves the problem of how to get rid of them with- 
out interfering with the valuable points already secured in 
dealing with other conditions. 

Operating at a distance, in order to produce parallelism 
of the rays, seems at present to be the only means of over- 
coming this phenomenon, but this, of course, bars out the use 

Fig. 42. 




INTERFERENCE OF PENUMBRA IN SHADOW TESTING. 

of many tests and methods which have been found of great 
service in uncovering ciliary spasm and latent errors, etc. Thus 
it will be seen that many contributing factors toward both 
success and failure enter into the problem of accurately estimat- 
ing the refraction of an eye "independent of a patient's 
intelligence/' 



CHAPTER V. 

Theory of Dynamic Skiametry, and the Importance of 
Reliable Fixation in Co-ordinate and Independent 
Observation, with a Reference to Three Essential 
Myopias, and an Explanation of "Ray Values." 

THEORY OF DYNAMIC SKIAMETRY. The optics of 
dynamic skiametry can be considered as being the same as the 
optics of static skiametry, one being fixation within infinity 
while the other is fixation at infinity. 

The word "dynamic" is derived from the Greek word 
dynamis, and signifies forces not in equilibrium, or motion as 
the result of force, being the opposite of "static." 

Dynamic skiametry then, as might be readily inferred, is 
an application of Bowman's discovery made under some kind 
of force. This force is the muscular one which is familiarly 
known as accommodation. 

While the static method of practising skiametry is one 
where the ciliary muscle of an eye is at rest, the dynamic 
method is the exact reverse of this, and is made while the 
accommodation is exerting itself sufficiently to readily accept 
refractive assistance up to a point where its relation with an- 
other muscular force called "convergence" is interfered with. 

The principle involved is a simple one. It is well known 
that a pound weight placed upon the shoulder of a sturdy 
man creates no appreciable burden or discomfort. But load 
this same man down to almost the limit of his endurance and 
then add this pound of additional weight and its presence will be 
noticed at once. So it is in dynamic skiametry, a call is made 
for a pronounced increase in tension of the accommodation 



THEORY OF DYNAMIC SKIAMETRY 8l 

by having the patient read a series of test letters placed either 
on an examiner's brow, attached to his skiascope, or to a fixa- 
tion stand, then, by varying this tension as judgment teaches 
and by being able to easily supply required artificial lens power, 
the accommodation is reduced to its normal relationship with 
convergence. And most eyes, no matter what the age of the 
patient may be, will only surrender the accommodative 
excess which has been required to maintain near-vision. This 
excess will therefore be composed of what has formerly been 
called by the name of "spasm" or "latent" hypermetropia. 

The relationship between accommodation and convergence, 
if roughly stated, is found to be in about the proportion of one 
to three for the two eyes ; that is, when the accommodation is 
exerted to the extent of one diopter, the convergence required, 
according to Hartridge, is a little over one and one-half de- 
grees for each eye. This, of course, is subject to variation, 
for when the accommodation equals ten diopters the conver- 
gence is estimated to be slightly over eighteen degrees for 
each eye. 

Another way of viewing this is to consider that for every 
diopter of accommodation exerted there is a corresponding 
meter angle of convergence called for, and a meter angle is 
described as the angle created by an imaginary line drawn from 
an eye to a point forty inches away, where it crosses another 
line called the "median" which is drawn from midway be- 
tween the two eyes. Two meter angles converging at twenty 
inches away would then be in harmony with two diopters of 
accommodation, and so on. To prove that the relationship 
between the two factors governing ocular adjustment is reliable, 
and that eyes under normal conditions do not converge without 
accommodating, nor accommodate without converging, the fol- 
lowing simple experiment can be made : Take a person under 
forty years of age with known emmetropics and place him so 
that his eyes are exactly forty inches away from the smallest 



82 THEORY OF DYNAMIC SKIAMETRY 

test type which he can see to read at this distance, then while 
he is engaged in the act of reading add a half-diopter convex 
lens quantity to both eyes, and it will be noted that the print 
will be perceptibly blurred or dimmed. In making this experi- 
ment be absolutely sure that there is no latent error present, or 
the test will prove unreliable. 

Now this seems to show that the relationship between these 
two forces is a quantity adjusted finely enough to be relied 
upon, for without the control of the convergence the accom- 
modation would have immediately relaxed when the lens was 
added which took away the necessity for the amount of mus- 
cular exertion represented by the fraction of one diopter which 
the lens called for. 

'An understanding of this point is very essential, as it repre- 
sents the basic principle upon which the dynamic method is 
founded. It is well known that both accommodation and con- 
vergence are elastic quantities, as an emmetrope with normal 
accommodation can wear minus lenses up to the limit of his 
amplitude without producing diplopia, also that the adduction 
and abduction of orthophoric eyes run into large figures before 
the doubling of an object occurs. Hence it will be seen that 
the relationship between these two forces is liable to vary in 
accordance with the training received by the muscles controlling 
them. And these, in turn, by the innervation of the nerves that 
transmit the vitalizing impulses. 

Two elastic bands linked together, in which the strength of 
one may be double that of the other, will find a point of balance, 
or equality of resistance, if stretched to any degree whatsoever, 
therefore when it is borne in mind that accommodation and 
convergence always have an individual balance for every visual 
point for which they co-operate it can be understood why 
-fixed rules for adapting prisms must prove unreliable. 

A case in point may emphasize this: A person born with 
two diopters of hypermetropia is compelled to suppress six 



THEORY OF DYNAMIC SKIAMETRY 83 

degrees of convergence while looking at a distance, this becomes 
a sort of habit which, owing to the greater development of the 
ciliary muscles through more than ordinary use, requires a 
new standard of relationship to be maintained that is adapted to 
this special condition. 

It might be reasoned that there are two ways of correcting 
such a case as this, one by relieving the tension on the intrinsic 
muscles with lenses, and the other by adapting prisms for the 
aid of the extrinsic ones. In some cases perhaps both forms 
of relief are indicated, but in most cases the wise procedure is 
to correct the refractive defect and then, by time and develop- 
ment, train the weakened extrinsic muscles up to an approx- 
imate standard of "i to 3" relationship with the intrinsic ones. 

Most eyes have some kind of a refractive error, or else they 
are so placed in the head that their relative position as to 
pupillary distance is at fault, and for this reason there is a sort 
of individual equation in almost every case which calls for 
special judgment. And it is this individuality that causes one 
patient to fix upon sixteen inches as a comfortable reading 
point, while another person, of the same age, will select a 
twelve-inch point. 

It has been stated that accommodation is captain of the 
visual ship, but captains have other persons to boss them, the 
same as fleas are said to have "other fleas to bite them," etc. 
So convergence might be called first mate, as its influence is 
undoubtedly felt in the compromise that must occur for all 
binocular visual fixation points. If this was not the case then 
emmetropes would read with comfort with spheric lenses 
of plus three diopters at thirteen inches, no matter 
how young or old the person was. The facts are, however, 
that an emmetrope with abundant amplitude of accommodation 
resents even a quarter of a diopter of artificial lens aid when 
reading at any near point, and the reason therefor is because 
the natural locking point, if it can be called such, between 



8 4 



THEORY OF DYNAMIC SKIAMETRY 



accommodation and convergence has been interfered with. This 
natural locking point, or relationship, constitutes the foundation 
upon which dynamic skiametry rests, and it can be relied upon 
to automatically adjust itself to the proper refractive quantity 
for any given distance — habit, general health and muscle inner- 
vation considered. 

In the optical principles of static skiametry, as given in the 
previous chapter, it was required that the rays of light ema- 
nating from the retina of a patient's eye have a conjugate focus 
or, in other words, that true or false myopia be present in 

Fig. 43. 




Myopic f.D 



Skiascope 



TRUE MYOPIA (STATIC METHOD) 



order to measure it, and thus to secure data upon w r hich other 
calculations can be based. Fig. 43 shows an eye with true 
myopia of one diopter, hence emerging rays of light come to a 
natural focus forty inches away. 

False myopia can be of two kinds, artificial and accommo- 
dative. Artificial myopia is produced by using a plus spheric 
trial lens, and accommodative myopia is temporarily acquired 
by having the patient look at a fixation object. 

By the static method it is required that a one-diopter trial 
lens be employed when the working distance is forty inches 
away, so that artificial myopia may be produced and the 



THEORY OF DYNAMIC SKIAMETRY 85 

emerging rays from an eye made to focus, or cross one 
another, at the focal length of the lens used. This is correct 
for this method, but for the dynamic method no trial lens is 
required to produce this false myopia, as the crystalline lens 
of the eye under examination takes its place. Fig. 44 will 
perhaps make this plainer, for in the drawing the false myopia 
under the static method is created by means of a trial lens, the 
eye being emmetropic and the rays emerging parallel before 
being refracted by the plus 1. D. trial lens. 

Fig. 44. 




fmm&irop/G. 

ARTIFICIAL MYOPIA (STATIC METHOD). 

Under the dynamic method, Fig. 45, the false myopia 
is created by means of an increase in the convexity of the 
crystalline lens, better known by the term accommodation, 
or "punctum accommodation" as Burnett calls it, the vision 
being fixed on some nearby object. 

This eye, the same as in Fig. 44, is emmetropic, thus making 
the two working conditions practically equal. 

By the static method, if the test is to be made at ten inches, a 
four-diopter , convex lens must be used. By the dynamic 
method this four-diopter convex lens power can virtually be 
added to the crystalline lens of the eye tinder examination by 
advancing the fixation card of the examiner up to a distance 



86 THEORY OF DYNAMIC SKIAMETRY 

of ten inches from the eyes of the patient, thereby causing the 
accommodation to be exerted to this degree in order that the 
letters on the card may be distinctly read; this effort, or the 
result of it, is why it is termed accommodative myopia, as dis- 
tinguished from the lenticular or artificial kind produced by the 
trial lens. 

To illustrate the value of this method, and also to show 
its practical adaptation, a case will be considered whose error 
of refraction is two diopters of hypermetropia, one diopter of 
which is manifest, and one diopter latent, or in a condition 

Fig. 45. 




Accommodation /D. 

Skiascope. 

ACCOMMODATIVE MYOPIA (DYNAMIC METHOD). 

somewhat spasmodic. In examining this eye at a distance of 
forty inches, the patient looking at some object twenty or more 
feet away, it is found that the static method shows one diopter 
of hyperopia, as it takes a two-diopter convex lens to produce a 
reversal of the shadow at this distance, one diopter of which 
represents the artificial myopia, or the working refraction re- 
quired. The dynamic method being used in this case, it is dis- 
covered that when the patient looks at the fixation card, forty 
inches away, a convex lens of a diopter and a half can be added 
before a reversal of the shadow is obtained, the examiner then 
advances so as to make the test at a distance of thirteen inches 
and finds that two diopters can be added before reversal takes 



THEORY OF DYNAMIC SKIAMETRY 87 

place. Advancing to within ten inches of the patient's eyes 
makes no change. Withdrawing to forty inches again, it is 
found that very little alteration in appearance of the shadow 
has occurred unless the patient has looked away in the mean- 
time, when the spasm will most likely reassert itself. 

Now what has taken place? The accommodation called 
for by the dynamic method at forty inches was one diopter. 
The patient having two diopters of hypermetropia had, there- 
fore, to make a total accommodative effort of three diopters, 
in order to see the letters on the fixation card. The examiner 
supplies refractive assistance until one diopter and a half of 
convex lens quantity has been added, the accommodation relax- 
ing to this degree and the shadow showing a reverse movement. 
Perhaps this case is one where the age of the patient is less 
than twenty years, general health considered good, and muscle 
tension, or unconscious habit of exertion, is suspected of being 
vigorous. A new test is made at a distance of thirteen inches 
where the total accommodation called for is five diopters, of 
which two represent the hyperopia and three the amount called 
for in emmetropia at this distance. Under this burden the eye 
will be found to accept a two-diopter convex lens quantity be- 
fore reversal occurs. Repeating the test again at ten inches no 
more relaxation is found, thereby proving the second finding 
to be correct. 

To analyze still further, it may be stated that at thirteen 
inches, where an emmetrope uses three diopters of accommo- 
dation, nine degrees of convergence are called for. A patient, 
therefore, who is making five diopters of accommodative effort, 
ought, correspondingly, to make fifteen degrees of convergence, 
thus calling for a distance of eight inches. 

So, as before stated, while both accommodation and con- 
vergence seem somewhat elastic they, nevertheless, appear to 
have a tendency to attain a standard co-ordination when dis- 
turbing factors are removed. 



88 



THEORY OF DYNAMIC SKIAMETRY 



Fig. 46 is intended to illustrate the mechanical action of 
a spasm of accommodation equal to a half-diopter. The line 
"a" shows the position of the lens when the accommodation 
is at rest. The line "b" shows its position when the accommoda- 
tion is equal to a half-diopter of involuntary effort, called 
"spasm" and the dotted line "c" shows when the accommodation 
is equal to one diopter. 

Fig. 46. 







HOW THE ACCOMMODATION CAN ABSORB A CILIARY SPASM. 



If the spasm, or unconscious muscle effort, equals a half- 
diopter, and the patient be required to look at an object which 
calls for one diopter of accommodation, then the conscious effort 
will, of course, be equal to the difference, or one half-diopter 
more. It can thus be seen that a spasm may be gotten rid of 
by what might be fittingly termed absorption. 

In applying this method to cases where the spasm is likely 
to be greater than one diopter, such as in children, or in those 
cases when heterophoria is present, the test should be 
made at a shorter distance than forty inches. Twenty inches, 
for instance, calling for two diopters of accommodation, ten 
inches for four diopters, and so on. 



THEORY OF DYNAMIC SKIAMETRY 89 

Another view for the elimination of spasm by the dynamic 
method can be taken : A man is told that he owes one dol- 
lar which he is desired to pay. He consults his books and finds 
that he has already paid fifty cents of this amount. Then all 
that can be righteously collected of him is the difference, or the 
remaining fifty cents. Now this same man consults an optome- 
trist, and is required to exert his accommodation equal to 
one diopter, but having a spasm of a half-diopter — and ocular 
spasms, as it is known, are really unconscious muscular efforts 
— he has, therefore, unknowingly contributed a half-diopter of 
accommodation which constitutes one-half of the amount re- 
quested of him, so he thus needs to consciously add a half- 
diopter more and the request is fully complied with. If his 
obligation, or error, had been higher the request would have 
had to be greater, but the principle is the same, and so when it 
comes to actual tests made by this method it will be found that 
the theories here expounded will be borne out in practice. 

Spasms of accommodation are now generally classified 
under two heads — the tonic, or persistent muscle effort, which 
is often called latent hypermetropia, and the clonic, or inter- 
mittent action of the ciliary, which is frequently met with in 
the objective estimation of both hypermetropia and myopia, 
particularly the latter. Both kinds, however, are factors in 
ocular skiametry of which cognizance must be taken and 
methods used whereby their disturbing 1 influence can be 
overcome. 

It is a rule that in persons over forty years of age, ski- 
ametric findings made by the static method are fairly reliable, 
but the drawback to the universal use of this one method lies 
in the inability of an examiner to differentiate his cases and to 
tell in advance whether he is dealing with a Case wherein spasm 
of accommodation is a factor until after he has used the dynamic 
method and compared results. Therefore, to save time and 
avoid error, it is wisd for an operator to use the dynamic method 



90 RELIABLE FIXATION 

in all cases under fifty years of age; and where the patient is 
under thirty it is best to use this method at as close a point as 
from ten to thirteen inches away. 

RELIABLE FIXATION. This subject, which has a 
direct bearing upon the question of brightness of the fundus 
reflex and corresponding definition of the pupillary shadow, 
relates to the visual angle under which examinations should 
be made, also to the point at which the patient's accommodation 
is to be adjusted during the observations. The point of reversal 
of a shadow is a very difficult one to decide upon with any great 
degree of exactness, for the reason that at the precise crossing 
point of the returning rays the shadow is most erratic and very 
difficult of determination as to its action. And as no lens 
power can be added to or subtracted from a patient's accommo- 
dation without interference with this action, it will readily be 
seen that the examiner's mirror must be operated either inside 
or outside of a patient's exact point of fixation if the behavior 
of the shadow is to be accentuated. 

In other words, if a patient is looking at a point exactly 
fifty-three inches away, and an examiner makes his observa- 
tion from a point forty inches distant, the shadow will show a 
hyperopic movement equal to a quarter of a diopter. On the 
other hand, if the examiner views this same eye from this 
same distance of forty inches, the patient, however, being re- 
quired to look at a card situated thirty-two inches away, the 
shadow's action will be a myopic one of a quarter of a diopter. 
Fig. 47 will perhaps make this plainer, for here it will be seen 
that the adjustment of the patient's accommodation was first 
made for a distance equal to three-quarters of a diopter, and 
then for a distance equal to a diopter and a quarter, the observer 
being at a distance of one diopter in both cases, the action of 
the shadow was, therefore, first with the mirror and then against 
it, whereas if a test had been made at one diopter the shadow, 



RELIABLE FIXATION 91 

of course, would not have shown any motion. Thus it will be 
seen that the method is not unlike solving the question of the 
exact middle of a piece of string by simply doubling it, for this 
is what it practically amounts to. 

In estimating the behavior of the shadow the advantage 
gained by an examiner in making his estimate from two or 
three focal adjustments of his patient's accommodation is, of 
course, just double or treble that of making it from a single 
point. Besides, it frequently occurs that an examiner desires 
to approximately ascertain the amount of any myopia present 
before he changes his lenses. All he has to do, then, is to 

Fig. 47. 




MULTIPLE FIXATION AND OBSERVATION POINTS. 

advance his mirror nearer to his patient while the latter is still 
looking at the forty-inch fixation point. If he finds that the 
shadow does not reverse until the mirror is advanced to within 
twenty inches of the eye under examination, then he knows 
that the myopia present is about two diopters, one of which 
represents the error and the other the accommodation. And if 
he has to advance up to within ten inches before obtaining a 
reversal he then knows that the error is nearer to three diopters, 
and so on. 

The means for accomplishing these results are very simple 
indeed. Fig. 48 shows a fixation stand, and the manner of its 
construction which, as can be seen, is merely a light-weight 
nickel-plated brass stand carrying a card having dots upon it 



92 



INITIAL EXAMINATIONS 



which the patient is asked to count. The stand being movable, 
and adjustable as to height, permits of its usefulness in 
many ways. 

Fig. 49 shows the style of card this stand can carry, on 
the reverse side of which is printed a small astigmatic dial, Fig. 

Fig. 48. 




AUTHOR S FIXATION STAND. 

50, which is merely a convenience to be used in other tests not 
concerned with skiametry. This stand, however, can be made 
to do excellent duty as a dynamic astigmometer ; enabling sub- 
jective measurements to be taken at any near point desired. 

INITIAL EXAMINATIONS. In initial skiametric tests 
the card, Fig. 49, is usually placed about a foot behind an ex- 
aminer's head, several inches to his right, and high enough for 



INITIAL EXAMINATIONS 



93 



its dots to be illuminated by the light source used, Fig. 51, 
showing the relative position of light, examiner, patient and 
fixation card. 

In operation the examiner requests his patient to first look 
at the dots on the fixation card, fifty-three inches away. In 

Fig. 49. 




Count the Dots. 

FIXATION-STAND TARGET CARD. 



Fig. 50. 
no &° 90 K*> 2% 




REVERSE SIDE OF FIXATION CARD. 

making his lens changes he stops with the shadow moving 
slightly with the mirror, then he requests the patient to look 
at fixation target cards on his skiascope. If he gets a reversal 
of the shadow he knows that he is very close to a correction for 
this distance. He then proceeds to finish the test and eliminate 



94 



INITIAL EXAMINATIONS 



the presence of any ciliary spasm by moving the mirror and its 
targets nearer to the patient, and at the same time crowding on 
all the convex lens quantity possible without producing an 
against motion. 

The card on the fixation stand may be used in place of the 
skiascope card for the shorter focal tests, but it will not be found 
as convenient. The greatest advantage to be derived from the 
employment of the fixation stand, however, lies in the angle at 
which an eye can be viewed, also in the apparent brilliancy and 
enlargement of the patient's pupil, which is due, no doubt, to a 



Fig. 51. 




fiATieuT 



POSITION FOR INITIAL EXAMINATION. 



Ci*& 



corresponding decrease in light stimulation. But, be that as it 
may, the use of the fixation stand in most cases is productive of 
much better initial results than accrue when its use is dispensed 
with. Especially is this true where the examiner is somewhat 
lacking in the experience which comes only with years of 
practice. 

The system of multiple cards, or fixation points, has an 
added value to an examiner from the fact that it enables him to 
make the first observation of a patient's eye under the most 
favorable conditions possible for obtaining a bright fundus 
reflex. He can then govern himself accordingly in further 
examination of the case. 



RAY VALUES 95 

If the reflex is a bright one, the change of vision from 
stand to skiascope card will not materially affect its brilliancy. 
On the other hand, if the reflex is poor then further tests 
should be continued by aid of the stand, which, being light 
in weight, its position can be easily altered by the examiner. 

There is another very valuable feature connected with the 
use of independent fixation points, and that is in the estimation 
of weak errors of refraction by instructing a patient to look 
back and forth from skiascope to fixation stand while the dis- 
tance of these two from the patient's eye differs slightly. 

RAY VALUES. The term "ray" is used in preference to 
the term "wave," simply for purposes of easy explanation and 
ready comprehension; therefore, from the foregoing, it will be 
understood how important it is for an examiner to have 
a thorough knowledge of ray values as well as of lens values. 
And by "ray values'" is meant the strength of the lens that 
would be required to parallel a ray of light when intercepted 
at any distance from its source. Fig. 2 in the first chapter 
emphasizes this principle. The value of a ray ten inches from 
its source is 4. D. ; at thirteen inches, 3. D. ; at sixteen inches, 
2.50 D. ; at twenty inches, 2. D. ; at twenty-six inches, 1.50 D. ; 
at forty inches, 1. D., and so on. 

In using both static and dynamic skiametry the position 
of an examiner and the dioptric values of his lenses in their 
relation to his patient's visual fixation are all factors in the 
correct estimation of ocular errors. Thus, if a patient is look- 
ing at an object situated eighty inches distant, and a skiametric 
examination is made at forty inches away, the ray value at 
eighty inches may be said to equal a half-diopter, while its value 
at forty inches is one diopter ; one less a half leaves a half, and 
the shadow under these conditions will behave as though the 
error were a half-diopter of hypermetropia. 

If the patient was looking at an object forty inches away. 



M" 



96 RAY VALUES 

and the examiner viewed the eye through the skiascope at a 
distance of eighty inches, then the reverse would of course 
be the case, and the error indicated would be a half-diopter 
of myopia. 

All of this, however, presupposes that the examiner knows 
just what his patient's accommodation is doing, and so by 
having fixation cards situated at forty, fifty-three, eighty, one 
hundred and sixty, and three hundred and twenty inches away, 
respectively, it would be possible for an examiner working 
at one meter to observe the shadow's action in the four quar- 
ters of a diopter of hypermetropia. This would necessitate the 
securing of an especially intelligent and obedient patient, to- 
gether with expert skill on the part of an examiner. 

Later on it will be seen that other methods can be used, 
where the intelligence of the patient is not so important a factor. 
The same principle governing ray values, however, can be 
applied to shorter distances. Thus, a patient with a one-diopter 
convex trial lens before his eye, when looking at a fixation 
card forty inches away, can be measured for a quarter, a half, 
or three-quarters of a diopter of hypermetropia, if the exam- 
iner will carefully measure the distances from his patient's 
eye so as to hold his mirror exactly thirty-two inches away 
when he is measuring for three-quarters of a diopter, twenty- 
six inches away when he is measuring for a half, twenty-two 
inches away when he is measuring for a quarter, and so on, 
the ray value modifying the lens value and the two combined 
influencing the total. In fact, in skiametry the determination of 
ray values can perhaps be summed up by deducting the value 
of what the ray is actually doing from what it really ought to 
do under the circumstances. 

The possibilities in the way of juggling with accommoda- 
tion, lens values, ray values and the shadow, are almost limit- 
less, and it is to be expected that as ocular skiametry and its 
methods become better known there will be found many more 



RAY VALUES 97 

ways of applying its principles which may not be all fully 
understood at this time. As the student acquaints himself 
with the principles involved in ray and lens values, however, he 
will find that the practical side of his work can be made much 
easier. The following examples, too, may show the applica- 
tion of some of the more important points : When an eye looks 
at an object situated forty inches away it must exert its accom- 
modation at least one diopter. Place a plus one-diopter 
spherical lens over this eye and if it is emmetropic the emergent 
rays will converge at a point twenty inches away. One diopter 
will then represent the accommodation, and one diopter the trial 
lens, or artificial myopia, making a total of two. If a plus two- 
diopter lens is used, the point of convergence will be at thirteen 
inches; if a plus three-diopter is employed, it will be at ten 
inches ; the accommodative myopia increasing the total myopia. 

Now suppose a patient has an error of two diopters of 
hypermetropia, then what occurs when a three-diopter lens 
is added? Why, the accommodation under the stress of 
carrying a burden immediately surrenders its error, read- 
justs its accommodation and convergence to a relationship of 
least resistance, and there is left only one diopter of what we 
call artificial myopia, and one of accommodative myopia. The 
point of convergence of the emergent rays would then be at 
twenty inches, instead of at ten inches, which would be the 
point of crossing of the rays from an emmetropic eye under 
the same conditions of lens and accommodation. Therefore it 
will be seen that where the rays ought to cross is at ten inches, 
and where they do cross is at twenty. The difference in ray 
value being two diopters — the amount of the error. 

In cases of this kind it is only natural for a student to ask 
why an eye under these conditions does not surrender more 
than two diopters, especially when it is exerting its accommo- 
dation one diopter for fixation. In reply it can be said that, 
without compulsion, an eye which is making three degrees of 



98 RAY VALUES 

convergence will naturally try to make one diopter of accommo- 
dation in order to maintain the harmony of the theoretic stand- 
ard of one to three relationship. This explanation can also be 
given to account for the discomfort an emmetrope of, say, 
twenty years of age, experiences when attempting to read at 
thirteen inches distance with a pair of half-diopter plus spheric 
lenses on, his accommodation and convergence will not be in 
accord. The convergence required at thirteen inches is nine 
degrees, which calls for a co-ordination of three diopters of 
accommodation, but try to reduce this accommodation by even 
a quarter-diopter and the harmony will be disturbed, causing 
discomfort to manifest itself. 

In true myopia, of one diopter, similar conditions of ray 
and fixation values are present, one diopter for accommodation 
at forty inches, and one for the true myopia, make two, the 
ray value of which is twenty inches. In all pronounced errors 
of refraction an examiner must ever bear in mind that the 
relationship of one: to three between accommodation and 
convergence may have been upset, and a different co-ordi- 
nation established. Measurements in myopic cases frequently 
vary under ray and lens value procedure, but while skiametry 
always gives the refraction exactly as it is under the existing 
conditions, these conditions may be such as to trouble an 
examiner in the formation of his judgment. Hence measure- 
ments taken in different ways are productive of better results. 

In measuring cases by ray values a student can work out 
any combination if he is well grounded in these principles. 
Simple, compound or mixed cases of astigmia are merely to 
be solved by measurement of meridians, as for instance: An 
eye having one diopter of hyperopic astigmia, axis vertical, in 
fixing at forty inches with a plus one-diopter spheric lens 
before it would show reversal of the shadow in the horizontal 
meridian at forty inches, and at twenty in the vertical. 



RAY VALUES 99 

In a myopic eye represented by the correcting formula of 
minus I. D. S. combined with minus i. D. C. axis 180 and 
fixing at, say, twenty inches, reversal would occur in the 
vertical meridian at ten inches and in the horizontal at thirteen. 
The student can therefore see that the whole subject is practi- 
cally one of figures, where axis and error are always to be con- 
sidered as at right angles to one another, and that myopia may 
be classified as of three kinds : true, accommodative and artificial. 



CHAPTER VI. 

Orthophoric and Heterophoric Conditions, and the In- 
fluence of Habit Upon Accommodation and Con- 
vergence, With Special Consideration of Spasms and 
the Use of Prisms. 

ORTHOPHORIA AND HETEROPHORIA. In order 
to again emphasize the strong points of dynamic skiametry it 
will be wise to further consider ocular muscle action and note 
its relation to other factors that are involved in the production 
of binocular vision, both with and without so-called strain. 

The perfect balance of the extrinsic muscles, termed ortho- 
phoria, is a rare condition, because with orthophoria there must, 
theoretically, be emmetropic, and experienced examiners know 
that scarcely one eye in a hundred is truly emmetropic. There- 
fore the concomitant of ametropia, as will be seen later on, is 
heterophoria, for, owing to the distribution of the ocular nerves, 
a single impulse would seem to affect both the intrinsic and 
extrinsic muscles in a co-ordinate manner, unless unconscious 
habits have been formed whereby one muscle action can be 
suppressed while another is exerted, even though the nerve 
supply is the same. Now this involves the question: What is 
a muscle and why does it act? So, without making the subject 
too lengthy, the dictionary may be briefly quoted as stating that 
a muscle is an organ composed of contractile fibres, through 
the contraction of <zvhich bodily movement is effected. These 
muscles are classified as voluntary, involuntary and mixed, the 
voluntary being subject to the will, the involuntary acting inde- 
pendent of the will, and the mixed combining in some degree 
the functions of both the others. 



INFLUENCE OF HABIT IOI 

All muscles are made to contract by means of nerves, 
and a nerve is described as a cord-like structure composed of 
delicate -filaments through which sensations, or stimulation im- 
pulses, are transmitted to and from the brain. These impulses 
being an expression of what is called nervous energy, which 
represents the active principle of organic life, this nerve action 
being dependent for its existence upon warmth, food and the 
orderly performance of the functions of the body. It will be 
seen, then, that this question is much like the ancient's descrip- 
tion of wisdom, which was represented as a serpent with its 
tail in its mouth, for the reasoning resembles a circle, no be- 
ginning or ending, since the nervous energy seems to reproduce 
itself. In other words, it takes health to make nervous energy, 
and nervous energy to make health. 

INFLUENCE OF HABIT. As before referred to, ocular 
habits of adjustment are factors to be reckoned with in the 
adaptation of glasses, for it is not difficult to understand that 
if an eye has been exerting its accommodation for many years 
in overcoming an error, like hypermetropia, the convergence 
has had to form special habits, too, in order to harmonize with 
the accommodation. Then when glasses are given for the cor- 
rection of the hypermetropia it follows that convergence must 
be re-educated and adapted to the new relationship. 

Prof. William James says that "habit has a physical 
basis" and, that "the moment that one tries to define what 
habit is, one is led to the fundamental properties of matter." 
He further says that the phenomena of habit in living beings 
are due to the plasticity of the organic materials of which their 
bodies are composed, and that the philosophy of habit at bottom 
is a physical principle and therefore belongs to physics rather 
than to physiology or psychology. 

Leon Dumont says: "Every one knows how a garment, 
after having been worn a certain time, clings to the shape of 



102 INFLUENCE OF HABIT 

the body better than when it was new, and so in the nervous 
system the impressions fashion for themselves appropriate 
brain paths." 

Muscle habits are really brain habits, and of habits in gen- 
eral Professor James can be quoted still further, he says : "Habit 
is what keeps us all within the bounds of ordinance, and saves 
the children of fortune from the envious uprisings of the poor. 
It alone prevents the hardest and most repulsive walks of life 
from being deserted by those brought up to tread therein. It 
keeps the fisherman and the deck-hand at sea through the 
winter ; it holds the miner in his darkness, and nails the country- 
man to his log-cabin and his lonely farm through all the months 
of snow; it protects us from invasion by the natives of the 
desert and the frozen zone. It dooms us all to fight out the 
battle of life upon the lines of our nurture or our early choice, 
and to make the best of a pursuit that disagrees, because there 
is no other for which we are fitted, and it is too late to begin 
again. It keeps different social strata from mixing. Already 
at the age of twenty-five you see the professional mannerism 
settling down on the young commercial traveler, on the young 
doctor, on the young minister, on the young counsellor-at-law. 
You see the little lines of cleavage running through the char- 
acter, the tricks of thought, the prejudices, the ways of the 
'shop,' in a word, from which the man can by-and-by no 
more escape than his coat sleeve can suddenly fall into a new 
set of folds. On the whole, it is best he should not escape. 
It is well for the world that in most of us, by the age of thirty, 
the character has set like plaster, and will never soften again. 

"If the period between twenty and thirty is the critical one in 
the formation of intellectual and professional habits, the period 
below twenty is more important still for the fixing of personal 
habits, properly so called, such as vocalization and pronuncia- 
tion, gesture, motion, and address. Hardly ever is a language 
learned after twenty spoken without a foreign accent; hardly 



INFLUENCE OF HABIT IO3 

ever can a youth transferred to the society of his betters un- 
learn the nasality and other vices of speech bred in him by the 
associations of his growing years. Hardly ever, indeed, no 
matter how much money there be in his pocket, can he even 
learn to dress like a gentleman-born. The merchants offer their 
wares as eagerly to him as to the veriest 'swell/ but he simply 
cannot buy the right things. An invisible law, as strong as 
gravitation, keeps him within his orbit, arrayed this year as he 
was the last; and how his better-clad acquaintances contrive to 
get the things they wear will be for him a mystery till his 
dying day. 

"The great thing, then, in all education, is to make our 
nervous system our ally instead of our enemy. It is to fund 
and capitalize our acquisitions, and live at ease upon the inter- 
est of the fund. For this we must make automatic and ha- 
bitual, as early as possible, as many useful actions as we can, 
and guard against the growing into ways that are likely to be 
disadvantageous to us, as we should guard against the plague. 
The more of the details of our daily life we can hand over to 
the effortless custody of automatism, the more our higher 
powers of mind will be set free for their own proper work." 

The influence of habit upon our ocular functions is very 
strong indeed, as in most cases we are able through muscular 
effort to adapt ourselves to our visual necessities, even though 
we unconsciously pay a price in what is called "nervous strain." 
A hypermetrope in accommodating for his error is not unlike 
a man in walking with his feet turned outward at too great an 
angle, for, while both are possible for a period to time, yet con- 
tinued effort will eventually be productive of bad results. 
Habits of seeing under proper refractive and muscular adjust- 
ments should be acquired by all at as early an age as will prove 
practicable for a person to wear glasses. 

Figs. 52, 54 and 56 are designed to diagrammatically illus- 
trate the relationship between accommodation and convergence 



^■H 



104 



INFLUENCE OF HABIT 



in emmetropic, hypermetropic! and myopia, while Figs. 53, 55 
and 57 may give some idea of the nervous adjustment required 
to meet the ocular needs, from the standpoint of innervation 
and enervation. 

Fig. 52 is intended to show, by means of converging lines, 
the normal balance in an emmetropic eye between the muscles 
governing accommodation and those controlling convergence. 

Here it will be seen that the harmony between these two 
factors necessary to binocular vision is in accord, and that the 

Fig. 52. 

EMMET RO PIA 
0.$. ' 




0.0. 



BALANCING THE ACCOMMODATION AND CONVERGENCE IN 
EMMETROPIA. 



lines representing accommodation and convergence meet at a 
common point on another imaginary line called the median, 
which extends forward from midway between the two eyes, 
the innervation of course being directed toward the internal 
rectus and the ciliary muscles of each eye. 

Fig. 53 is designed to show a pair of thermometer-like 
tubes which, for convenience, might be styled a neurometer, 
these tubes being filled with an imaginary vital fluid repre- 
senting the nervous energy required to maintain the action of 
accommodation and convergence. The darts are to call atten- 



INFLUENCE OF HABIT IO5 

tion to the height of the fluid in the two columns, and to show 
the relative amount of nervous expenditure necessary to main- 
tain requisite muscle effort. Thus in emmetropia the darts 
seem to be equal and indicate that whatever the proportionate 
relationship really is, it remains a quantity that can be con- 
sidered as constant. 

In Fig. 54 may be seen the disturbed relation between 
accommodation and convergence which would take place in 
hypermetropia if the innervation was normal, as shown in Fig. 

Fig. 53. 



U 



EQUAL INNERVATION NECESSARY TO BALANCE ACCOMMODATION 
AND CONVERGENCE IN EMMETROPIA. 

53. Thus esophoria and the origin of convergent strabismus 
can be surmised. 

In Fig. 53 the darts, "A" and "C," show that binocular vis- 
ion would be impossible under these conditions, and so individ- 
uals having eyes of this kind must learn to either decrease 
convergence or increase accommodation in an independent 
manner. This relative effort is shown by the position of the 
darts in the neurometer, Fig. 55, the nervous impulse here 
being much greater for accommodation. 

In Fig. 56 the lack of harmony between darts "A" and "C" 
indicates that in myopia accommodation must be decreased or 
convergence increased before the two can be brought together. 



io6 



INFLUENCE OF HABIT 



Fig. 57 shows a relative adjustment of innervation to which 
nature undoubtedly resorts in cases of this kind. 

With an understanding of the disturbance in innervation 
which a hypermetrope or myope has to make in order to con- 



Fig. 54. 
HYPERMETROPJA 




O.o. [ 



imbalance of accommodation and convergence in hyper- 

metropia. 



Fig. 55. 




UNEQUAL INNERVATION REQUIRED TO BALANCE ACCOMMODATION 
AND CONVERGENCE IN HYPERMETROPIC. 



stantly maintain binocular vision, it is quite easy to see how 
readily an individual can form habits of muscular action con- 
trolling accommodation and convergence which would prove 
most difficult of reformation. And this leads the reasoner to 



INFLUENCE OF HABIT 



I07 



a general consideration of so-called "spasms," "latent errors" 
"muscular insufficiencies" etc., etc. 

It also serves to emphasize the importance of keeping errors 
of refraction under constant correction, thereby enabling indi- 

Fig. 56. 

MYOPIA 
o.s. 




0.0. 



imbalance of accommodation and convergence in myopia. 

Fig. 57. 




UNEQUAL INNERVATION REQUIRED TO BALANCE ACCOMMODATION 
AND CONVERGENCE IN MYOPIA. 

viduals to form new ocular muscle habits which will be in 
accord with standard visual requirements. Then, too, it will 
show the wisdom of postponing the adaptation of prisms until 
after old habits have been broken up by altering the conditions 
responsible for them. 



108 CILIARY SPASMS 

CILIARY SPASMS, ETC. In arguing against the use 
of cycloplegics some optometrists are inclined to question the 
frequency of spasms and latent errors and to contend that their 
importance is overestimated, but familiarity with static and 
dynamic skiametry will soon prove the contrary. Spasms are 
defined as : "Involuntary convulsive contraction of muscles" 
and "convulsion" in turn, is described as "irregular and violent 
commotion" Now, this latter definition might perhaps be modi- 
fied a little and thereby convey a somewhat better understand- 
ing of the term spasm, as it is used here. 

Owing to the contractile quality of muscles, they can only 
do one thing, and that is to pull, not push. Therefore, when 
the term "violent commotion" is used, it is immediately asso- 
ciated with the idea of a rapid and intense muscular activity, 
which resembles the seizures of epilepsy, and wrong impressions 
are apt to be formed. 

As before stated, spasms can be of two kinds — the steady 
and the vacillating. So, where the word tonic is used in con- 
nection with them, they are to be associated with the idea of 
an unconscious, involuntary, regular, steady and persistent 
muscle tension. 

Where the word clonic is used, however, it should be under- 
stood to mean unconscious, involuntary, irregular, contracting 
and relaxing muscle action, which, when taken in connection 
with the so-called accommodation of an eye, may be either 
rapid or slow in its operation. 

The term tonic spasm of accommodation, as understood 
to-day, bears a close resemblance to what many readers of 
Donders are led to infer from his use of the term "latent" in 
connection with hypermetropia, for the word "tonus," from 
which the word "tonic" is derived, signifies an involuntary 
condition which might be likened to increased vigor or tone 
in a muscle whereby it may insist on doing more work than 
is really intended for it. This, of course, is alike applicable 



CILIARY SPASMS IO9 

to myopic and emmetropic eyes, though not occurring with the 
same frequency as in hypermetropic ones. 

The cause of these spasms is also a varying one. In hyper- 
metropic, the constant muscle tension required in order to 
maintain vision is no doubt a pronounced factor. In myopia 
and in emmetropia an uncontrollable supply of nervous energy 
actuating the muscles is probably one reason for their invol- 
untary contraction. Occupation, too, which leads to the for- 
mation of muscle habits, is undoubtedly another cause, and so 
quite a number of reasons might be suggested. The work of 
the optometrist, however, deals only with the determination 
of their presence and the estimation of their strength or influ- 
ence on the refraction of an eye. 

Reference has been made to the use of a local toxicant, 
technically termed a "cycloplegic" which is employed to par- 
alyze the muscle action of an eye, but the drawbacks attendant 
upon the use of this means are so many, both from a practical 
as well as a theoretical standpoint, that some method had to 
be devised in order to eliminate the guess work which must 
necessarily enter into all cases where the exact refraction of an 
eye at its reading or working point is not known. And by 
"exact refraction" is meant the muscle tonus, or muscle inner- 
vation, which constitutes an individual factor in each case. 

By subjective methods, if the patient is of sufficient intelli- 
gence and shows the proper amount of interest in the case, a 
cross-examination in connection with other tests will enable 
an examiner to form a fairly satisfactory idea of the range of 
accommodation, and from this known range he can make a 
close estimate as to the strength of the glasses required. But 
by the method known as dynamic skiametry a more certain 
estimate can frequently be arrived at, for by this examination 
the burden of judgment is shifted from the shoulders of the 



IIO CILIARY SPASMS 

patient to those of the examiner who, as his experience in- 
creases, should be a better judge of his patient's needs than 
the patient himself. 

In the dynamic method attention has been called to the 
fact that where the muscles controlling accommodation were 
heavily taxed it was easy to see how readily they might be 
induced to surrender any excess of energy which they had 
hitherto concealed, no matter whether this concealment was 
total, in the form of a tonic muscle effort, or intermittent in 
the form of a clonic one. 

Attention will be invited in another chapter to the advan- 
tages to be derived from the use of mobile, rather than of 
fixed, lens values, and this may serve to make this point plainer, 
for spasms of accommodation, especially of the clonic variety, 
require a lens action which will in a measure imitate the in- 
crease and decrease in convexity of the crystalline lens of an 
eye itself. To deal successfully with spasms, an examiner 
must, therefore, use some means which will enable him to 
make his lens changes in a gradual, rapid and accurate manner, 
and at the same time operate at any desired distance from his 
patient. 

Then, too, if habits are to be broken up, the patient must 
be required to make some refractive adjustment that is unusual, 
and differing from the manner in which his eyes have been 
generally employed. 

Many persons with uncorrected hypermetropia use their 
eyes as little as possible for reading or near work. Their 
muscle adjustment for distance, however, is almost a constant 
quantity during their waking hours. If such a person is 
young, and the ocular muscle action is vigorous, a static test, 
without cycloplegia, made at twenty feet is very likely to un- 
cover only a portion of the error, for the reason that the 



CILIARY SPASMS III 

accommodation muscles have been so in the habit of exerting 
themselves at this distance that when lenses are supplied which 
remove the necessity for this exertion these muscles seem to 
refuse much of the assistance offered them. 

On the other hand, if this case is examined skiascopically 
at a distance nearer than that of the usual reading point, it 
will be observed that the eye will now accept lenses very much 
stronger, for here habit is not such a factor, and under the 
burden of increased muscle effort the accommodation will 
readily give up the excess tension which it was so accustomed 
to exert for distant uses. Thus, habit being temporarily broken, 
the muscles governing accommodation and convergence are 
more likely to assume standard relations, and especially so if 
a lens system is used which permits of binocular mobile action. 

In myopia, particularly in those cases which have remained 
uncorrected for a number of years, the accommodation is 
likely to prove disappointing in its action by behaving either 
spasmodically or quite the reverse. For this reason greater 
care must be exercised, when measuring these cases, to employ 
corroborative methods. A myopic case can seemingly be 
readily changed into a hypermetropic one by over-correction 
of the error, but muscle habits formed through ordinary occu- 
pations cannot be changed in a minute, and this fact must ever 
control the judgment of an examiner and cause him to adopt 
such methods and measures as will give him the fullest informa- 
tion regarding the requirements of each and every case that 
presents itself. 

Of the two forces, accommodation and convergence, the 
former is probably the controlling one. So-called "muscular 
insufficiencies" are, therefore, doubtless the result of inco- 
ordination between the ciliary and the recti groups. If the 
theories as illustrated by Figs. 52 to 57, inclusive, are correct 
ones, then the fallacy of adapting prisms for the purpose of 
permanently assisting the muscles controlling convergence is 



112 CILIARY SPASMS 

made plain for many cases, for where the error of refraction 
is not fully corrected it is logical to expect that the muscles 
controlling convergence will not behave in accordance with 
standards which are applicable only in emmetropia. 

Where the recti muscles are mal-attached to the eyeball, 
or where there is a permanent deficiency in the amount of 
their innervation, then prisms would seem to be indicated, but 
experience teaches that these cases are rare. It is wise, then, 
for an examiner to correct his patient's refraction first and 
wait for the muscles governing accommodation and convergence 
to adapt themselves to the new order of things. If they fail to 
do this, and the examiner is sure that the error of refraction 
is fully corrected, then, and only then, is he warranted in the 
use of prisms, unless for the accomplishment of some tempo- 
rary result. 

While adduction, abduction and sursumduction offer import- 
ant data by which to aid an examiner's judgment, they are 
usually of little avail until after emmetropia has been estab- 
lished and maintained long enough for accommodation, con- 
vergence and innervation to have ordinarily acquired a habit 
indicative of normal muscle balance. 

To make these points plain it can be seen that if the rela- 
tive proportion of three degrees of convergence, or one meter 
angle, to one diopter of accommodation is taken as a standard 
of estimation, then eyes having one diopter of hypermetropia 
in reading at a distance of sixteen inches away, which calls 
for two and a half diopters more, must make an accommodative 
effort equal to three and one-half diopters in all. 

This ciliary action would call for a harmonious conver- 
gence equal to about ten degrees, and ten degrees, in turn, 
would call for a reading distance of eleven inches away, thus 
showing that while the eyes were accommodating for sixteen 
inches they would really have to converge to a point five inches 



CILIARY SPASMS 113 

nearer in order to use a standard or proportionate amount of 
nervous energy; and as this would be quite impossible without 
disturbing binocular vision, hence the only other course left is 
for the innervation of the convergent muscles to be correspond- 
ingly decreased. 

As emmetropic eyes cannot alter their co-ordinate muscle 
action without previous training, it would seem to be reason- 
able to assume that ametropic eyes ought also to require an 
equal time and training in order to enable them to convert 
their latent errors, or those due to habits of suppression, into 
manifest ones, or those within the individual's own control. 

To what extent habit interferes with the accuracy of static 
skiametry must be left to the imagination of those examiners 
who have not yet had opportunities of personal observation. 
And while dynamic skiametry offers a marvelous improvement 
in estimating the true refractive errors of young persons, it, too, 
is frequently interfered with by this same disturbing factor of 
habit, or "individual equation/' as it is sometimes called. 

It must not be overlooked, however, that, even after latent 
errors have been determined, and spasms unlocked, it is not 
always wise to endeavor to force eye muscles to accept standard 
relationship in too short a period of time, for while it is true 
that usually the best results are obtained after emmetropic and 
orthophoria have been established, yet it is equally true that, 
in some cases, it is better to ignore a small spasm and permit 
the muscles to work, for a while, in excess of normal re- 
quirements. 

This, therefore, indicates that optometric findings are one 
thing and the judgment used in adapting glasses and prisms is 
quite another. For with the experienced examiner it often 
happens that in youthful cases he may find an error of perhaps 
four diopters of hypermetropia by the dynamic method, and yet 
correct only two diopters of this in the first glasses given, 
taking several months of time in order to educate the eye 



■M^MHMi^^^B^^BM^^^^ 



114 CILIARY SPASMS 

muscles up to a normal standard where they can bear a full 
correction of their refractive errors. 

The making of the original examination in a thorough and 
reliable manner will thus be seen to greatly assist an examiner 
in prognosticating his cases, as well as in giving advice the 
correctness of which will be borne out in due course of time. 

There is an old adage which says that "it takes a long time 
to teach old dogs new tricks/' and the reason for this lies, 
perhaps, in the fact that before new habits, or "tricks," can be 
formed the old ones must be broken up, and this in some cases 
may be more of a task than even the formation of the new. 
Spasmodic muscle action, while unimportant in some cases, is 
quite the contrary in others, so that the wise examiner will take 
no chances, but proceed to thoroughly master all of his cases. 
Any unsatisfactory results that may occur can then be at- 
tributed more to faulty judgment than to a lack of knowledge 
of the optical and correlated intrinsic and extrinsic muscle 
action involved. 



CHAPTER VII. 

Practice of Dynamic Skiametry, Its Use in Measuring 
Regular and Irregular Astigmia, and Its Special 
Value in the Objective Estimation of Presbyopia 
and Sub- Normal Accommodation, Together With Its 
Relationship to Other Methods and Tests. 

PRACTICE OF DYNAMIC SKIAMETRY. It is un- 
questionably true that no other one instrument in the arma- 
mentarium of an optometrist requires more practice to success- 
fully master than does the skiascope, and, it might be added 
that the dynamic method requires much greater skill in order 
to read the shadow's action than does that of the static. The 
reason for this is to be found in a consideration of the subject 
of retinal illumination, for it is well known that the shorter 
the distance between the light source and the patient's eye the 
larger and brighter will be the area of illumination on the 
fundus of the eye under examination. This, taken in connection 
with the optical laws regulating penumbra, and the variation 
in retinal pigmentation, together with size of ocular pupils, 
added to light stimulation, will show why the nearer a shadow 
test is made the more difficult becomes the reading. 

If it was not for the erratic relationship that frequently 
exists between accommodation and convergence, and for the 
irregularities existing in corneal curvatures, then the static 
method would be the best to use, and the greater the distance 
it was employed the better the results would be. But ski- 
ametry, like many other systems, has to be taken as it is, and 
not as the operator or patient would like to have it. 

Practice, plenty of practice, the same as one becomes expert 



^^^^^^^^^■■^^^■^^MH^^^^H^^H 



Il6 PRACTICE OF DYNAMIC SKIAMETRY 

in shooting a gun, or in making examinations by indirect 
ophthalmoscopy is the only way in which an examiner can 
become skillful in skiametry. The general variation in appear- 
ance of eyes is such that a comprehensive description of all 
kinds is almost impossible, the student must, therefore, see for 
himself. But to put into words a description of the procedure 
necessary in making an examination by the dynamic method 
the following may give a better understanding. 

In order to secure as favorable a fundus reflex as possible, 
place the fixation-stand target card forty inches from the pa- 
tient's eyes and then make the first skiascopic observation from 
a point about two or three inches to the left of this card and 
an inch or so nearer the patient. If motion against is not 
present then add plus spheric lenses until motion against occurs 
in some meridian. The strength of the lens next weaker than 
the one that just causes the against motion is the one that 
represents the error for this distance in the meridian measured. 

If, on the other hand, at the first observation an against 
motion is noted, then, with the patient still looking at the 
fixation-stand card, the examiner is to advance toward the 
patient until a with motion is obtained in some one meridian. 
This distance, estimated in diopters, less the i. D. of accommo- 
dative myopia, due to the forty-inch fixation, will represent the 
true myopia for the meridian measured, and if astigmia is 
present all the meridians will not measure alike. 

After this first estimation of the error, or errors, the exam- 
iner is to place the estimated correcting lenses in position on 
the patient's face and make a subjective test, after which he 
is to return to skiametry again and make another examination 
at a reading or much nearer point than the first one was made, 
using the fixation cards on his bracket skiascope. The changing 
back and forth from objective to subjective and from subjective 
to objective will be seen to give all the refractive data that it is 
possible to obtain, after which the use of other instruments and 



MEASURING ASTIGMIA BY SKIAMETRY W] 

methods may, or may not, be indicated, as their necessity is 
usually determined by the previous findings. 

Two typical cases may possibly make these points plainer: 
Case i. Age of patient, thirty years. Fixation, forty inches. 
Observation, thirty-nine inches. Shadow with the mirror. Can 
add plus i. D. before reversal occurs. Subjective test also 
shows i. D. of hyperopia. But with fixation and observation 
at sixteen inches, a total of plus 1.50 D. can be added before 
reversal takes place. Same result is obtained when -fixation 
and observation are at thirteen inches. Case 2. Age of patient, 
thirty years. Fixation, forty inches. Observation, thirty-nine 
inches. Shadow shows against the mirror. Reversal takes 
place at twenty inches which, after deducting 1. D. for the 
accommodative myopia at forty inches, leaves 1. D. of true 
myopia. Subjective test calls for a minus 1.50 D. S. lens.. 
Fixation and observation at sixteen inches show a with mo- 
tion with a minus 0.75 D. S. lens, and at thirteen inches a: 
minus 0.50 D. S. lens is the weakest one a with motion can be 
obtained with. The student must not forget, however, that 
data and prescription are not always one and the same. 

MEASURING REGULAR AND IRREGULAR AS- 
TIGMIA BY SKIAMETRY. The variation in the appear- 
ance of astigmatic eyes is often baffling to the skiametrist. 
Some shadows show an even edge that makes their measure- 
ment most easy, while others scatter and re-form several times 
in crossing over a pupil. The cause for this can perhaps be 
found in a consideration of scar tissue, for where reliable his- 
tory of many cases of this kind has been obtained it is found 
that in childhood the patient suffered from inflamed eyes, and 
the sequela was the irregularly thickened corneal tissue which 
manifests itself in unequal refraction. 

A study of these cases with the skiascope will often enable 
an examiner to cope with those which at first seem almost hope- 



Il8 MEASURING PRESBYOPIA BY SKIAMETRY 

less, and this rule holds good with all classes of skiametric 
cases, no matter what method is used. The skiametrist must 
simply perfect his skill by ample practice. 

When the conditions are ideal an examiner will be able 
to note a sort of straight edge action to the shadow. If the 
error is marked then this edge will be well defined, but if the 
error is slight then the edge will be difficult to note. 

In those cases where what is called the "scissors" movement 
appears an examiner will observe two shadows in one meridian, 
one with the mirror and the other against. This is frequently 
caused by making the observation too far to one side of the 
line of fixation, especially where the correcting lenses used are 
of high power. 

The generally accepted theory of the cause of the "scis- 
sors" movement attributes it to the crystalline lens being slightly 
askew in its capsule, but if an examiner will keep the lines of 
observation and fixation as near together as it is possible and 
obtain a good fundus reflex he will find that true crystalline 
displacements are quite rare. 

In partially opaque corneas, and in cases of cortical cataract 
where transparency is interfered with, an examiner will often 
be rewarded through results obtained by careful work with 
his skiascope. Cataracts in process of development can often 
be detected, too, long before the vision of the patient is per- 
ceptibly impaired. The spicula in the crystalline showing trans- 
lucent upon the red background of the pupil, and especially do 
they appear plain when mechanical mydriasis is made use of. 

MEASURING PRESBYOPIA BY SKIAMETRY. 
Presbyopia is usually regarded as an infirmity, rather than as 
an error of refraction, but it can also be considered in the latter 
light, too, for research proves that the crystalline changes begin 
almost at birth and continue all through life. Loss of elasticity 
due to changes in density and to production of an altered 



MEASURING PRESBYOPIA BY SKIAMETRY II9 

index surely indicate refractive variations, and as the only dif- 
ference between lenses of like kind is variation in ray-bending 
power, therefore presbyopia would seem to rightfully belong 
under the classification of refractive anomalies, just as much as 
under accommodative anomalies. 

Presbyopia is the one, so-called, "easy" ocular condition 
that is often the most difficult of satisfactory correction, for the 
reason that occupation, illumination, habit, pupillary distance 
and innervation, or bodily vigor, are all factors to be reckoned 
with. Then, if combined with this the ignorance and stupidity 
of many patients in answering questions is taken into consid- 
eration, it is easy to see why changes in reading glasses are 
so frequent when "there's nothing the matter with the eyes." 

Up to the time of the development of the dynamic method 
of practising skiametry there was no known method of estimat- 
ing presbyopia in an objective manner. All static methods, 
whether with or without cycloplegia, are solely for determining 
the refractive condition of an eye while its muscles are in a 
state of complete relaxation, therefore the static method gives 
no definite aid in presbyopia whatsoever. 

Dynamic skiametry supplies the refractionist with a method 
that often proves of the very greatest aid in mastering a 
troublesome case, as it enables the eyes to be studied at all 
points, near as well as distant, this study being directed toward 
steadiness of convergence and accommodation, both of which 
can be detected through the use of a skiascope and lenses. As 
illustrative of this, suppose a case presents itself having a 
history of discomfort in reading, etc., the patient is directed to 
look at the skiascope fixation-card fourteen inches away while 
plus one-diopter spheric lenses are before each eye. If right 
eye shows a with motion while left eye is against, it indicates 
either an error of refraction or an unequal innervation of the 
muscles controlling accommodation, notwithstanding that at 
infinity both error and vision seemed alike in the two eyes. The 



120 SUB-NORMAL ACCOMMODATION 

use of the mirror at this distance also enables the detection of 
any deviation in convergence of either eye when fixation for 
this point is maintained for a considerable time. 

It is conceded, of course, that it takes more skiametric skill 
to measure an eye at fourteen inches than it does at forty, but 
that which is possible for one examiner is also possible for 
another with equal intelligence and perseverance. Dynamic ski- 
ametry being particularly adapted to the needs of those who 
are advanced in optometric knowledge and skill. 

SUB-NORMAL ACCOMMODATION. In comparatively 
recent years that which was formerly called "latent" hyperme- 
tropia has been classed as an early or sub-normal accommoda- 
tion, and practitioners of repute are now adapting bi-focal 
lenses to young persons with great success in some cases. 

To the optometrist it matters little whether the patient's 
inability to see nearby objects is caused by latent hypermetropia 
or by an early change in the index of refraction of the crys- 
talline, or by a weakened muscle action, what he needs to know 
is the true condition of the refraction at all points, near and 
distant, and then by keeping the patient under observation it 
can be determined whether the case is one requiring the aid of 
the family physician or of the ophthalmic specialist. 

As in presbyopia, dynamic skiametry instantly detects a lag 
in accommodation, and if this "lag" is present it needs looking 
after. 

A case is reported of a young Miss, fifteen years old, who 
was behind in her school work. She had been atropinized and 
fitted with O. ,U. plus I. D. S. lenses for constant use. So- 
called iC retinoscopy, } ' in the hands of an optometrist who 
thought well of his own ability, confirmed the findings of the 
oculist who prescribed the glasses. Static skiametry also con- 
firmed the prescription given. Dynamic skiametry, however, 
showed that a plus 3. D. S. lens was indicated at thirteen 



OTHER TESTS 121 

inches. Plus 2. D. S. lenses, O. U. worn for a month did not 
succeed in relaxing any more than the original correction for 
infinity. Bi-focals of plus 1. D. S. upper and plus 3. D. S. 
lower gave almost perfect results after this form of glass had 
been worn a few weeks. Adduction and abduction were both 
poor, but the eyes were orthophoric. If dynamic skiametry had 
not been used in this case the chances are that it would have 
gone the way of many others, and the patient allowed to 
suffer on. 

Perhaps a stronger cycloplegic, or a long period of wearing 
fogging lenses would have revealed more latent error, but the 
indications were that this was a case of what is termed "pre- 
mature presbyopia" or "sub-normal accommodation'' and 
dynamic skiametry was the only method by which it could be 
intelligently refracted. 

OTHER TESTS. It may do no harm to repeat once 
more that no one optometric test is the "whole thing/' as the 
urchins say. The definition of the word optometry, it must not 
be forgotten, is eye-measuring. That of skiametry is shadow- 
measuring, and as the word ocular means eye, it will therefore 
be seen that ocular-skiametry is only one division of optometry, 
and that the dynamic method constitutes merely a sub-division. 

If all divisions of a subject bear an integral relation to the 
whole, then dynamic skiametry is but one means for obtaining 
data which, together with that secured by other methods, con- 
tributes to the formulation of the proper prescription, and 
"proper prescription" means the glasses that are best for the 
patient to use. Thus, if by subjective measurement the patient 
says that his vision is improved by the use of a convex spheric 
lens of two diopters, but by keratometry a mal-curvature of a 
half-diopter of the cornea is shown, and by dynamic skiametry 
a three-diopter convex spheric is called for, then it may be wise 
to prescribe a two and one-half sphere, especially if the patient 



122 OTHER TESTS 

has been wearing a partial correction and gives a history of 
eye-strain. 

It is the combination of important factors in a given case 
that often makes success possible. Blind adherence to any one 
test, or method, is no doubt responsible for many optometric 
failures. Duction tests of the muscles give data that have great 
influence in determining the strength of lenses to be prescribed, 
even though prisms are not used, and where heterophoria is 
present the data secured by means of dynamic skiametry may 
often save the prescribing of prisms. 

The aim of the thorough-going optometrist should be to 
determine as carefully as possible the true condition of his 
patient's eyes. And this involves many tests in some 
cases and few in others, for a case of simple presbyopia, with 
standard vision and no history of discomfort, does not need the 
time nor the many tests that are indicated where the ametropia 
is complex and the history of general health and nervousness 
poor. 

Of course the treatment of impaired health of a patient is 
foreign to the service that an optometrist is generally consulted 
for, but a "poor history" forms data that has an indirect bear- 
ing upon all optometric cases, so the wise examiner acquaints 
himself with all tests and methods that will aid him in the for- 
mation of correct judgment, for, after all, it is this "judgment" 
which makes one succeed where another fails. 

Perhaps one of the hardest strains a new method has to 
stand is the extravagant claims made for it by enthusiasts. 
Take the keratometer for instance, a very valuable instrument 
but often most unreliable where its findings are blindly adhered 
to. One great mistake made by many practitioners of op- 
tometry is that they do not take their profession seriously 
enough. It seems so easy to use a few instruments, ask a ques- 
tion or two and then form snap judgment as to a patient's 



OTHER TESTS 1 23 

requirements, therefore it is little wonder that this field attracts 
to it many incompetents. 

As optometry develops, however, it is hoped that the general 
public will grow wiser and learn to reward those who give the 
time and make the effort to fully master each and every detail 
that has direct and indirect bearing upon the practice of 
optometry in its larger sense. 



CHAPTER VIII. 

Illustrative Cases, Showing the Comparative Value of 
Static and Dynamic Skiametry in Patients of Dif- 
ferent Ages, Occupation and General Physical 
Condition. 

ILLUSTRATIVE CASES. The expression "Figures 
talk" is especially applicable in describing the relative merits of 
static and dynamic methods in practising ocular skiametry. 
Space, therefore, will here be devoted to descriptions of various 
cases for the purpose of emphasizing points already alluded 
to, and of incidentally calling attention to the influence of 
occupation and the importance which attaches to the condi- 
tion of the patient's general health. All the examinations 
referred to were made without the aid of cycloplegics, conse- 
quently the static test mentioned is the non-toxic kind. 

CASE A. 

Master S., age 7. In school. Health, seemingly good; 
O. S. shows slight convergent squint. 

Vision = O. D. 20/20. O. S. 20/100. 

Static test = O. D. + 2.50 D. S. O. S. + 3. D. S. 

Dynamic test at forty inches = O. U. + 3-5° D. S. 

Dynamic test at twenty inches = O. U. + 4. D. S. 

Dynamic test at thirteen inches == Unsatisfactory. 

Trial case test = O. D. + 2. D. S. O. S. + 3. D. S. 

Vision = O. D. 20/20. O. D. 20/80. 

Formula given = O. U. + 3. D. S. for constant use, with 

instructions to return in one year. 



ILLUSTRATIVE CASES 1 25 

Two years later O. U. + 3.50 D. S. was readily accepted. 

No squint. 

Vision = O. D. 20/20. O. S. 20/40. 

CASE B. 

Master W., age 11. Health not rugged. Inability to see 
blackboard. 

Vision = O. U. 20/100. Static test = O. U. — 1. D. S. 

Dynamic test at 13 inches = O. U. — 0.50 D. S. 

Trial case test — O. U. — 1.25 D. S. 

Vision = 20/20 in both eyes. 

Formula given = O. U. — 0.50 D. S. for constant use. 

Instructed to return in three months. 

Six months later vision O. U. = 20/20 with 
O. D. — 0.75 — D. S. 
O. S. — 0.75 — D. S. 



CASE C. 
Miss N., age 16. In school. Health fair. Headaches. 

Vision = O. U. 20/30. 

Static test = O. U. + 0.50 D. C. 90 . 

Dynamic test at 16 inches, same. 

Trial case test = O. U. — 0.50 D. C. 180 . 

Vision = 20/20 in both eyes. 

Formula given = O. U. + 0.50 D. C. 90 . 

Vision = "misty." 

Instructed to use at study, and oftener if more comfortable. 
Later on she reported "no headaches," and vision was found 
to be 20/20 with glasses. 



^aaaaaamamaamamaamm 



126 ILLUSTRATIVE CASES 

CASE D. 

Mr. G., age 20. In college. Reports his health good. No 
discomfort, but "can't see at a distance/' 

Vision = O. U. 20/200. 

Static test = O. U. — 2.50 D. S. 

Dynamic test at 40 inches = O. U. — 2. D. S. 

At 16 inches, about the same. 

Trial case test = O. U. — 2.75 D. S. 

Vision = 20/20 in both eyes. 

Formula given = O. U. — 2. D. S. for constant use. 

Instructed to return if he had any further trouble. No report. 

CASE E. 

Mr. S., age 24. Mechanic. Something of an athlete; com- 
plains of headache. 

Vision O. U. == 20/20. 

Static test O. U. = + 1.25 D. S. C + 0.25 D. C. 90 . 

Dynamic test at 13 inches = 

O. U. = + 2. D. S. C + 0.25 D. C. 90 . 

Trial case test O. U. = .+ 1. D. S. C + 0.37 D. C. 90 . 

Vision = 20/20. 

Formula given O. U. = + 1. D. S. C + 0.25 D. C. 90 . 

Advised to return in one year, which he did, and was given 

O. U. = + 1.50 D. S. C + 0.25 D. C. 90 . 

Advised to return again within two years. 

CASE F. 

Miss F., age 26. Seamstress. General health not good. 
"Weak eyes." 

Vision = O. D. 20/40. O. S. 20/80. 
Has been using O. U. + I. D. S. 



ILLUSTRATIVE CASES 12J 

Static test = 

O. D. + 0.50 D. S. C + 2. D. C. 90 . 

O. S. + 2. D. S. C + 2. D. C. 105 . 

Dynamic test at 40 inches = 

O. D. + 1. D. S. C + 2. D. C. 90 . 

O. S. + 3. D. S. C + 2. D. C. 105 . 

Dynamic test at 20 inches = 

O. D. + 1.50 D, S. C + 2. D. C. 90 . 

O. S. + 3. D. S. C + 2. D. C. 105 . 

Dynamic test at 13 inches = Sam' 

Keratometer — O. D. 2. D. 90 . O. S. 2. D. no°. 

(Note difference in axis of O. S. 

Trial case test = 

O. D. + 0.25 D. S. C + 2. D. C. 90 . 

O. S. + 1.50 D. S. C + 2. D. C. 105 . 

Vision = O. D. 20/20. O. S. 20/40. 

Formula given = 

O. D. + 1. D. S. C ■ + 2. D. C. 90 . 

O. S. + 2.50 D. S. C + 2. D. C. 105 °. 

Instructed to wear constantly and to "never mind if distant 
objects are a trifle blurred for a few weeks." Returned in a 
week with a history of occasional discomfort. Gave advice to 
persevere. Returned in four months with a broken lens and 
wanted a new one "immediately." Glasses were very satis- 
factory. Vision == O. D. 20/20. O. S. 20/40. 

CASE G. 

Mr. C., age 29. Bookkeeper. Reports health good when 
not working too hard. Eyes and head "feel bad" afternoons. 
Has been wearing glasses for three years of the following 
formula : 

O. D. — 1. D. S. C .+ 2. D. C. 75 . 
O. S. — 1. D. S. C + i-5o D. C. 105 . 



■^^■■■^■^IB^HiHHHi 



128 ILLUSTRATIVE CASES 

Vision with present glasses = O. U. 20/30. 

Fundus reflex very poor. 

Keratometer shows = O. D. 2. D. axis 75 °. O. S. 2. D. axis 105 °. 

Dynamic test at thirteen inches, with trial lenses, shows the 

myopic quantity to be only 0.50 D. in both eyes. 

Trial case test = 

O. D. — 1. D. S. C + 2. D. C. 75°. 

O. S. — 1. D. S. C + 2. D. C. 105 . 

Vision = 20/30. 



Formula 


given = 












O. D. — 


0.50 D. S. 


C + 2. 


D. 


C. 


75°. 




O. S. — 


0.50 D. S. 


C + 2. 


D. 


C. 


105°. 




Vision = 


: "Foggy." 












Report received in 


two weeks: 


"All right 


now." 



CASE H. 

Mr. R., age 34. Grocer. History of health unsatisfactory. 
Vision poor for past few months. 

Present vision = 20/80 in both eyes. 

Static test = 

O. D. + 1. D. S. C + 0.50 D. C. 180 . 

O. S. + 1. D. S. C + 0.50 D. C. 180 . 

Dynamic tests, at 40 and 16 inches, about the same. Trial case, 

about the same. 

Optical correction no material aid to vision. Ophthalmo- 
scope shows pale discs. Close questioning leads to conclusion 
that it is a probable case of nicotine poisoning, due to immod- 
erate smoking aggravated by the moderate use of alcohol. Gave 
no glasses. Advised to consult an oculist first. 

CASE J. 

Miss B., age 38. Stenographer. Says health is good except 
for headaches. 



ILLUSTRATIVE CASES 1 29 

Vision = O. U. 20/20. 

Static test = O, U. + 0.50 D. S. 

Dynamic tests at 40 and 16 inches = O. U. + °-75 D. S. 

Trial case test = O. U. + 0.25 D. S. 

Vision = 20/20 trifle "hazy." 

Formula given — O. U. .+ 0.50 D. S. 

For reading and near work. Good report. 

CASE K. 

Mrs. A., age 41. Has household cares only. General health 
none too good. Complains of inability to see to thread her 
needle and do fancy work. No headaches. 

Vision == O. U. 20/20. 

Dynamic tests at 40 and 16 inches = O. U. + 1. D. S. 

Trial case test = O. U. + 0.75 D. S. 

Vision = 20/20. 

Formula given = -J- 1. D. S. for both eyes. 

Instructed to use for near work. No report. 

CASE L. 
Mrs. L., age 46. Housekeeper. Health appears good. 
Difficulty in reading. No headache. 
Vision = O. U. 20/20. 
Static test = O. U. + 0.25 D. C. 90 . 

Dynamic test, at 40 inches, about the same. Trial case, about 
the same. 

Dynamic test at 15 inches = + 1. D. 

Formula given = O. U. + 1. D. S. C + 0.25 D. C. 90 for 
reading, etc. No report. 

CASE M. 
Mr. D., age 52. Court stenographer. Health seemingly 
good. Never has had any glasses that proved quite satis- 
factory. 



^^IMB^M 



130 ILLUSTRATIVE CASES 

Vision = O. U. 20/80. Dynamic test at 50 inches = 

O. D. + 1.25 D. S. C+ 0.25 D. C. 135°. 

O. S. + 1-25 D. S. C + 0.25 D. C. go . 

Trial case test, the same. Vision = O. U. 20/30. 

Presbyopia = 2.25 D. Gave bi-focals. 

Reported in sixty days that vision was good but glasses did 

not seem quite right. "Guessed" he was working too hard. 

Re-examination by dynamic test at 30 inches = 

O. D. + 1.50 D. S. C + 0.25 D. C. 120 . 

O. S. + 1.75 D. S. C + 0.25 D. C. 8o°. 

Vision = O. U. 20/20. 

Presbyopia = 2. D. 

Reported in six months "O. K. now, 'twas the glasses after all." 

CASE N. 

Mr. O'B., age 55. Driver. Health good. "Can't see." 

Vision = O. U. 20/80. Static test = O. U. + 1.50 D. S. 

Presbyopia = 2.50 D. 

Trial case test = O. U. + I -5° D. S. 

Vision = 20/20. 

Formula given = O. U. + 4. D. S. for reading. Would not 

wear distance correction. 

No report. 

CASE O. 

Mr. E., age 59. Tailor and cutter. Health good. Working 
distance about twenty inches away. Present glasses are -f- 3. 
D. S. for both eyes, and are not very satisfactory. 

Vision = O. D. 20/30. O. S. 20/100. 

Static test — 

O. D. + 0.50 D. S. 

O. S. + 1. D. S. + 1. D. C. 180 . 



ILLUSTRATIVE CASES 13 1 

Keratometer shows no corneal mal-curvature in either eye. 

Trial case test, same as static test. 

Vision = O. D. 20/20. O. S. 20/40. 

Presbyopia at working distance = 2. D. 

Presbyopia at reading distance = 2.75 D. 

Formula for working glasses = 

O. D. + 2.50 D. S. 

O. S. + 3. D. S. + 1. D. C. 180 . 

Formula for reading glasses = 

O. D. + 3.25 D. S. 

O. S. + 375 D. S. + 1. D. C. 180 . 

Instructed to return if not satisfactory. No report. 

CASE P. 

Mrs. M., age 62. Occupation (?). Health (?). Looks 
well. 

Vision less than 20/200 in both eyes. 

Static test : First attempt, no retinal reflex. Without skiameter 
the mirror shows small pupils and slow plus movement. With 
skiameter, lenses being set to enlarge the pupils, better move- 
ment is obtained and long, narrow, spike-like patches show. 
Error about + 4. D. S. in both eyes. 
Trial case test = O. U. + 3.50 D. S. 
Vision = O. D. 20/40. O. S. 20/60. 
Presbyopia = 3. D. 

Ophthalmoscope shows slight cortical cataracts. 
Gave formulas: Distance ==: O. U. + 3.50 D. S. 
Reading = O. U. + 6.50 D. S. 

With instructions to be sure and have a strong light coming 
over shoulder when reading or sewing. Sent letter to family 
physician. 



132 



ILLUSTRATIVE CASES 



CASE Q. 

Mr. McE., age 67, Health fair. Retired. Now using 
glasses + 4. D. S. for reading; wonders if they can be im- 
proved. 

Vision = O. U. 20/80, which is improved by partially closing 
the eyelids. Static test — O. U. + 1 - D. S. Trial case test the 
same. Vision = O. U. 20/30. Presbyopia = -j- 3. D. S. 
Formula for distance = + J - D. S. Advised to continue with 
present reading glasses and to increase his illumination when 
using his eyes for near purposes. No report. 

Note. — According to Donders the near point of distinct vision 
in an emmetropic eye is as follows : 



At 10 
" 20 


years 


of age 


it is 2^4 
4 


inches away 
it it 


30 

" 40 
" 50 

" 60 


a 


a it 

tt (C 


« « 5 y 2 

" « 9 
" " 16 
" " 40 


Si tt 

ti (( 



To illustrate in fuller detail the workings of dynamic ski- 
ametry, let the following case be analyzed. 

Mr. H., age 25. Contractor's timekeeper. Leads outdoor 
life. General health excellent. Complains of occasional 
headache. 

Vision = O. U. 20/20. Static test = O. U. + 1.25 D. S. 
Dynamic test at 13 inches = O. U. + 2. D. S. 
Trial case test = O. U. + 1. D. S. Vision = 20/20. 

By reference to Fig. 54, it will be seen that when his accom- 
modation and convergence each receive an equal amount of 
innervation, the convergence will be greater than the accommo- 
dation, and binocular confusion will result, thus giving rise to 
esophoria unless the innervation is altered in some way so as 



ILLUSTRATIVE CASES 133 

to produce the condition called for by Fig. 55, where the 
innervation for accommodation is in excess of that for con- 
vergence. A test of his extrinsic muscles, however, shows a 
manifest orthophoria without glasses. 

Now what are the deductions to be drawn from this case? 
Twenty-five years of daily use of the eyes without glasses has 
established a habit of adjustment whereby the standard rela- 
tionship between accommodation and convergence has been re- 
placed by a condition in which convergence has given way a 
little, otherwise esophoria would have manifested itself. 

The static test shows a reversal of the shadow when over one 
and a quarter diopters of convex lens power are added. This 
is in addition, of course, to the quantity necessary to create 
the artificial myopia. Thus proving that habit has not mastered 
quite all of the error, as the accommodation readily accepts 
partial assistance and relaxes its muscle tension as much as 
five-eighths of the full ametropia present. The remaining three- 
eighths of the total error can be called latent, but in reality it 
represents a tonic spasm, a knowledge of the presence of which 
materially aids an examiner in the formation of his judgment 
and in the advice and prognosis he is enabled to give a patient. 

To determine the amount of tonic spasm present in a case, 
such as the one under consideration, it will be necessary to 
resort to the dynamic method which calls for a pronounced 
exertion of the patient's accommodation. 

An emmetrope twenty-five years of age is supposed to have 
about eight diopters of amplitude of accommodation. The near- 
est point of distinct vision is then five inches away from the 
eyes. A dynamic test made at thirteen inches calls for an ac- 
commodation equal to three diopters. The patient's error being 
two diopters, it follows that a total ocular muscle exertion equal 
to five diopters is necessary in order to enable the patient to dis- 
tinctly read small letters on a card whose distance away is the 
same as that of the examiner's mirror. 



134 ILLUSTRATIVE CASES 

More than five diopters of accommodative effort can, of 
course, be exerted by the patient in this case. Yet this amount 
will generally be found quite sufficient to break up any tonic 
spasm, or habit of muscle exertion, that may have been formed. 
Five diopters less three diopters leaves two diopters, and a lens 
quantity of this strength should reverse the shadow by the 
dynamic test under these conditions. 

If the test had been made at twenty inches, then four diop- 
ters would represent the total muscle effort called for. If at 
ten inches, then six diopters would be the full accommodation 
needed. The difference between these amounts and that re- 
quired to maintain normal relationship between accommodation 
and convergence at whatever distance the test is made will 
show at once in the lens quantity required to reverse the 
shadow, provided the eyes are examined in a semi-binocular 
manner, namely, first one eye and then the other, alternating fre- 
quently so as to insure an equality of visual fixation. 

One point which seems to puzzle many examiners who take 
an interest in making theory substantiate practice is to under- 
stand why an emmetropic eye when under an accommodative 
tension of three diopters at thirteeen inches, will not relax to 
two diopters when one diopter of assistance is offered it. The 
answer to this query probably lies in a better understanding of 
muscular co-ordination and innervation, for, as stated in earlier 
chapters, the eyes of a healthy person, free from coercion, 
cannot converge without accommodating, nor can they accom- 
modate without converging. And this co-ordinate relationship 
will respond to approximate standards unless long-standing 
abnormal requirements have induced irregular habits. In this 
latter case refractive measurements must be taken in such a 
manner as to estimate the real influence of these habits by mak- 
ing the eyes work, for the time being, in a manner as far 
removed from old beaten paths as possible. 



ILLUSTRATIVE CASES 1 35 

Now another case will be cited in order that the details of 
skiametric procedure may be accentuated. 

Mr. Z., age thirty-five, occupation watchmaker. Has been 
studying optics for two years. States that he has fitted himself 
with O. U. — 0.50 D. S. C — 0.75 D. C. axis 180 , that his 
vision without glasses is O. D. = 15/30 O. S. =15/20, and 
that he has four degrees of esophoria. 

As the above information, excepting the age, is supplied 
after the examination is finished, the examiner, of course, pro- 
ceeds in the usual manner and directs the patient to look at the 
letters on a fixation stand card situated fifty-three inches dis- 
tant. In an observation made at forty inches the examiner finds 
that in the right eye there is a fairly distinct edge to the shadow 
and that it points a little to the left of the vertical meridian. 
Adding convex lens quantity it is found that one diopter is 
needed to reverse the shadow in the horizontal meridian, and 
that in the vertical, with no lens power added, the motion is a 
trifle against the mirror. With the patient still looking at the 
fixation card fifty-three inches away the examiner finds that 
he must advance his mirror ten to fourteen inches nearer to his 
patient before he obtains a reversal of the shadow in this me- 
ridian. So he notes on his examination blank "O. D. — 0.25 
D. S. C + 1. D. C. axis 105." 

In the left eye the horizontal motion is reversed with a half- 
diopter convex lens quantity. In the vertical meridian there 
is a motion with the mirror, when the examiner is forty inches 
away. Adding even a slight convex lens power stops it. The 
axis seems to be about fifteen degrees to the temporal side of 
the head. The examiner notes "O. S. -f- 0.50 D. C. axis 75." 
Corroborating subjectively, it is found that vision O. U. 20/20, 
a trifle "misty," can be secured with O. D. — 0.50 D. S. 3 + 
0.75 D. C. axis 105 and O. S. + 0.25 D. C. axis 75. Patient 
reads well with this correction, and — 0.50 D. S. or + °-5° 
D. S. added in a binocular way offers no aid. Corroborating 



I36 ILLUSTRATIVE CASES 

skiametrically again with the full correction on, it is found that 
a quarter-diopter convex lens reverses the shadow in all merid- 
ians when the patient looks at the brow card on the examiner's 
mirror, no matter whether its distance be twenty or forty 
inches away. With the quarter-diopter convex lens power 
removed, the shadow shows a suggestion of a movement with 
the mirror, at the same distances of twenty and forty inches 
away. The above formula is then ordered and the patient is 
instructed to wear the glasses as much as possible and to report 
in a month. 

In analyzing this case the occupation of the patient is borne 
in mind as one calling for considerable accommodative adjust- 
ment. Then the previous wearing of concave lenses is perhaps 
partly responsible for the four degrees of esophoria complained 
of, for with these glasses on one end of the astigmatic interval 
in the left eye calls for one and a half-diopters of accommoda- 
tion which, in turn, calls for two and a quarter degrees of con- 
vergence in order to maintain standard co-ordination. And this 
for one eye only. 

The age of the patient, the habit of excessive convergence 
due to occupation, also the habit of accommodation aggravated 
by the occasional use of glasses calling for increased ciliary 
effort, are all factors to be considered by an examiner, espe- 
cially if his patient returns in a day or two and complains of a 
"thin fog," etc. 

The temptation to advise the immediate use of lenses which 
the optometrist feels sure represent the full correction of his 
patient's ametropia is very strong indeed, and if he has an 
intelligent patient to reason with this judgment is often correct. 
But if his patient happens to be of the timid kind, or one who 
thinks the acuity of vision to be had after one day's use of 
glasses is the only thing to judge their merits by, then it is 
wise to "make two bites of a cherry" and indulge the patient's 
own notions by giving a temporary correction slightly over or 



ILLUSTRATIVE CASES 1 37 

under that which is really indicated, and which will eventually 
have to be given. 

It is cases such as these that render the science of optometry 
inexact, for an examiner must always remember that attached 
to every pair of eyes is a different individual with a different 
body, a different occupation, different habits and different ideas 
as to different things, and so each patient requires, different 
judgment and different explanations and encouragements. 

And it is for these differences that in optometry, as in other 
specialties, "many are called and few are chosen." 



CHAPTER IX. 

Multiple Methods in Optometry and Their Value in 
Corroborative Measurements. — The Systematic 
Keeping of Records and the Importance of "Case 
History", Including Resourcefulness, and Mechani- 
cal Mydriasis. 

MULTIPLE METHODS. Eye-measuring embraces 
many "tnetrys" and the able optometrist must be master of them 
all. Even in the method to which the name static skiametry 
has been logically given there are many ways of applying its 
optical principles. The word "static," as is well known, is used 
to designate bodies at rest, or forces in equilibrium. The 
medical examiner attempts to induce this rest of the muscles, 
controlling the accommodation of an eye, by instilling into the 
cul-de-sac of this organ some one of a series of powerful 
toxicants, and thus, for the time being, practically transform- 
ing a living eye into a sort of schematic one. 

Non-medical examiners, on the other hand, attempt the 
relaxation of this accommodation by having their patients look 
toward some distant object in order to thus coax the muscles 
into a condition of inactivity, and in further explanation it may 
be truthfully said that in many cases one overdoes the matter 
while the other underdoes it. The medical examiner's over- 
doing consists in forcing the eye into an abnormal condition 
in which the co-ordination of accommodation and convergence 
is temporarily destroyed, this destruction depending of course 
upon the strength of the drug used, and the duration and fre- 
quency of its instillation, as well as upon the idiosyncrasies of 
the patient. The results obtained by measuring the refraction 



MULTIPLE METHODS 1 39 

of an eye while it is in a state of what might be called "local 
intoxication" would seem to call for judgment of the very 
highest type in order to make the theoretical conform to the 
practical. 

Regarding the non-medical examiner's manner of using the 
static method, especially in those cases where the muscle action 
is liable to be particularly vigorous, it can be likened to the 
old story of the blind leading the blind, for the reason that if the 
patient fails to maintain the requisite muscular relaxation the 
examiner has no means of knowing what action has really 
taken place, and his findings, therefore, are likely to prove very 
unreliable. 

Spasms of accommodation, as they are termed, are probably 
responsible for more mistakes being made in the non-toxic 
manner of employing the static method than can be attributed 
to the carelessness of patients in looking, or in trying to look, 
at the object to which their attention has been directed. 

In dealing with these cases there are two ways in which 
static skiametry can be used. One consists in beginning an 
examination with only that lens before the patient's eye which 
is necessary to produce the artificial myopia required for the 
operating distance, whatever that may be, and then, if the case 
is a hypermetropic one, the convex lenses are to be gradually 
increased in strength until the reversal point of the shadow is 
obtained. 

If the case is one of true myopia, however, then an over- 
correction is necessary, and the concave lenses used for this 
purpose are to be gradually decreased in strength until the 
reversal point of the shadow is found. This manner of increas- 
ing in hypermetropia and of decreasing in myopia is called the 
amplifying method. 

Overcorrecting in hyperopic cases and undercorrecting in 
myopic ones have been termed the fogging method. And where 
ocular skiametry is performed in a non-toxic manner this 



I4O MULTIPLE METHODS 

method of decreasing lens values in hypermetropic! and of in- 
creasing them in myopia will often prove of great assistance to 
an examiner, and especially so if applied in a binocular manner, 
for then the co-ordinate action of accommodation and conver- 
gence is such as to give the most reliable results. This, of course, 
includes more particularly those cases where the age of the 
patient is such as to lead an examiner to fear spasmodic muscle 
action. 

In cases of persons fifty years of age or older, wherein 
presbyopia has a tendency to overcome spasm of accommoda- 
tion, then static skiametry will frequently be found quite trust- 
worthy, but where the age of the patient is less than fifty years 
then a method more reliable must be used to determine true 
refractive conditions. 

In the toxic application of static skiametry it, of course, 
matters little whether the amplifying or fogging method is used, 
for here the accommodation is supposed to be in abeyance and 
the examiner can suit his own convenience in regard to the 
manner in which he alters his lens quantities. But the toxic 
method has disadvantages along many lines when it is viewed 
from both scientific and economic standpoints. In its scientific 
aspect it fails entirely to tell anything about muscle tension at 
the reading point, leaving this to be estimated and guessed at 
by the examiner, while this reading point, as is well known, 
constitutes one of the most important ends for which glasses are 
adapted. Frequently, too, for distance purposes a medical 
examiner is led to advise glasses from a theoretical instead of a 
practical knowledge of the true conditions present. 

All cycloplegics, as pointed out before, are of necessity 
mydriatics, and the mydriasis they produce constitutes a dis- 
turbing factor, causing the pupillary field to become so enlarged 
as to add to skiametric complications and to increase the diffi- 
culties of the method. 

Viewed from an economic standpoint the toxic method tends 



CORROBORATIVE MEASUREMENTS 141 

toward the needless distress of patients, causes a quite unneces- 
sary waste of valuable time, in waiting for the action of the 
cycloplegic, and takes a foolish chance, even if only a slight one, 
of risking a possibility of blindness resulting from glaucoma. 

Every working distance at which static skiametry is prac- 
ticed, whether by toxic or non-toxic means, really constitutes a 
method in itself, and for the reason that the nearer a patient's 
eye an examination is made the more carefully must the appear- 
ance of the shadow, as well as other features of the test, be 
studied. For instance, in an examination made at eighty inches 
a half-diopter convex working lens quantity would have to be 
placed before the patient's eyes in order to produce artificial 
myopia and focus the parallel rays of light emanating from the 
retina of an emmetrope. Here the behavior of the shadow 
would be much quicker, while its color and intensity would be 
more pronounced than if the test were made at forty inches, 
where a one-diopter convex working lens was used. 

A test made at forty inches might also prove very satis- 
factory, while one made at ten inches, using a four-diopter lens, 
might be anything but satisfactory, even in the same eye. Thus 
it will be seen that as a student delves deeper into the intricacies 
of skiametry the more complicated does the system seem and 
the more manifold do its methods appear. 

Experience, however, does wonders in developing skill and 
judgment, so that old examiners, as well as students, profit by 
constant every-day work, just as old users of the ophthalmoscope 
improve by daily practice with this valuable little instrument for 
scanning the ocular fundus. The truly wise, therefore, will 
never miss an opportunity to examine a case. 

CORROBORATIVE MEASUREMENTS. It is not so 
very long ago when to possess an optometer of simple make, or 
a modest trial case, seemed to be all that an examiner needed 
in order to cope with the requirements of his cases. But, thanks 



142 CORROBORATIVE MEASUREMENTS 

to the progressives, which include patients as well as examiners, 
that time has gone by and accuracy and attention to detail are 
now the order of the day in optometric practice. 

To do high-class work at the present time (and he who does 
not do it is pretty sure to be left in the race), an optometrist 
must be thoroughly familiar with the various methods and 
devices which have received the stamp of approval of those of 
recognized ability in this field. 

At first thought, it would seem as though the trial case 
ought to be given primary attention, on account of its age, but, 
logically, it should come last because it offers the nearest 
approach to an actual pair of glasses, and because, too, it 
practically gives the only means of determining binocular vision 
with any degree of satisfaction. 

To ocular skiametry, however, belongs the first place in 
the refractive scale, not from its priority of discovery, but 
rather from a utilitarian standpoint. It is not only the great 
pathfinder that points the way for other work, but it is also the 
great verifier that tells whether the other work is correct or not. 
In its most approved application it discloses minute opacities 
of the cornea and crystalline lens, thereby giving information at 
once which the ophthalmoscope could not locate except, possibly, 
after a long time-consuming hunt. 

It tells of the presence of astigmia, its character and approxi- 
mate axis, and also whether it is complicated with any error 
requiring the correction of spherical lenses. 

It shows refractive conditions independent of the patient's 
age, language or answers, and serves to check carelessness in 
all persons. 

In children it is of invaluable service, and in those whose 
hearing is faulty it saves much shouting and misunderstanding. 

Its use, therefore, comes at both the beginning of an exam- 
ination and at its end, and if astigmia of considerable amount 



CORROBORATIVE MEASUREMENTS 1 43 

is disclosed it is a source of satisfaction, though perhaps not 
absolutely necessary, to use a keratometer and endeavor to ob- 
jectively locate the exact axis of the error. Then following 
these methods it is well to ascertain, subjectively of course, 
whether vision is in harmony with refraction, if it be found 
otherwise then the ophthalmoscope should be employed to ascer- 
tain, if possible, why, and thus enable the optometrist to know 
whether the case is one calling for glasses, for medical treat- 
ment, or for both. 

If the vision and the refraction agree in a monocular manner, 
but not in a binocular one, then phorometric devices are to be 
called into requisition. Thus it will be seen that in the order of 
their use skiametry is first, keratometry second, trial-case lenses 
third, and then, if needed, ophthalmoscopy fourth, phorometry 
fifth and perimetry sixth. 

Three of these methods represent the objective, and three 
the subjective, so that practically all of the six methods are inter- 
dependent, the only one which might really be dispensed with 
being the cornea measure, and this it not advisable. 

In all-round optometric work the placing of sole depend- 
ence upon one method, one device, or one system, for success, 
is about as foolish as it would be to place like dependence 
upon one method, one device, or one system in the practice of 
any other professional calling, where the conditions are likely 
to vary in different cases. 

Then, too, the use of examination room apparatus, whose 
only value is to mystify patients and make them believe they 
are undergoing a thorough scientific examination, is a means 
hardly calculated to maintain that lasting public confidence 
which usually contributes to a long and increasing practice. 
Nor is it wise to idle away a patient's time in needless visual 
tests merely for the purpose of trying to create favorable 
impressions regarding professional ability, for there is now 
enough that is of real value in optometric work to gain, with 



144 SYSTEMATIC CASE RECORDS 

intelligent use, the confidence of educated as well as unedu- 
cated patrons. 

To attain the very highest order of practical scientific 
results should be the well defined aim of those who devote 
either all or part of their time and ability to the mastery of 
physiologic optics. And as a means to this end the practice 
of systematically corroborating all ocular measurements will 
be found to act as a preventive to the making of those mis- 
takes which, when discovered by some other examiner, are so 
difficult of explanation. 

SYSTEMATIC CASE RECORDS. As one of the pro- 
nounced aids to successful examination room work, a brief 
reference will here be made to systematic examinations and the 
practical assistance to be derived from carefully recording 
them. 

The great value of this troublesome detail can not be em- 
phasized too frequently for, as has been remarked before, ocu- 
lar skiametry is the great refractive pathfinder, and therefore 
when the path has once been found it is wise to keep it, and 
keep track of its various windings. 

A blank form should be used containing properly named 
spaces wherein entries can be systematically made, so that 
nothing of importance may be overlooked in the hurry of busy 
days. This blank should be large enough to contain on one 
sheet a complete record of everything pertaining to a case. 

This is an age of card indexes, and the makers of these 
valuable time-savers seem, at last, to appreciate the needs of 
those who are engaged in optometric work, for they now make 
their cards large enough to meet the optometrist's purposes, 
as shown by Fig. 58. 

This card is five inches wide by eight inches long, and is 
plain on the back so as to permit of space for entries covering 
repairing and changes. It is designed in such a manner as to 



systematic case records 
Fig. 58. 



145 



Date 

Name, 

Street, 

City 



Occupation. 



Ophthalmo- 
scopic 



OBJECTIVE 

Cornea I Irta 



Skia- 


0. D 


6 


Bph. 


, 


I Sph. 


33 



Sph. 


Cyl. 


Axis 


Kerato 




Ami. 


Axis 


metric 


0. S. 


M 




M 


|s 








metric 




Pheco- 
metric 


[ Sp2u 

O.D.1 




St 
Cyl. 


BJECTIVE 

Axis 


U. V. 


C. V. j Amp. 


Preeby. 


OS.) 










J 




Prism 0- 


CvD. 


Ad. 


" 


Sur. 


Ex. 


Es. 


Hyp. 




Case History 


metnc 


0. s. 































Previous Formula 



0. D. 



Ordered by_ 



_years 



P. D. 



.H'ght.. 



Facial Measurement 

Cr'st, Base,. 



.Head. 



Formula Prescribes 



For 


D. 


Sph. 


Cyl. 


Axis 


Prism 


Base 


Lenses 


Spg. 


Ocard 


H 


0. S. 










Mlg. 


Stud 


VnU 



For Bi-F. add. 



-Segs. 



.Price, $_ 







Lenses Spg. 



Ht» Bsar cot 



0. s. 



Sire of Lens. 

Total, $ 

Call 



Price, $. 



Amount Paid, $_ 



Amount Due. $_. 
Mail 



Fe».$u 



Referred by. 



Ex'm'd by. 



AUTHOR S RECORD BLANK. 



I46 SYSTEMATIC CASE RECORDS 

expedite examinations and to show at a glance whether con- 
ditions are usual or unusual. The space for case history while 
not large will be found ample when taken in connection with 
the preliminary findings. 

Generally speaking, "case history" covers only the symp- 
toms complained of by the patient but, broadly, all findings 
that serve as an aid to the formation of correct judgment 
constitute optometric case history in its true sense. 

The records, both old and new, which are made use of 
during the week also serve as a kind of day-book and thus in 
the end really save more labor, from a bookkeeping stand- 
point, than their use entails. 

To describe more completely the uses for which a record 
blank is intended it can be stated that the age of the patient 
may be marked in cipher, so that inquisitive persons cannot 
gratify idle curiosity if the record happens to be left care- 
lessly exposed. 

The examination covers "occupation," for it is important 
to know what kind of work the eyes are to be used for. Then 
follows the use of the ophthalmoscope and a cursory inspection 
of the lids, cornea, iris, lens and fundus. As the word opto- 
metric pertains to eye measuring in general it will be seen that 
eye measuring in detail ought, logically, to have its word 
terminals in metrics too, hence this rule has been followed as 
far as possible in the make-up of this blank. 

Skiametric covers both static and dynamic methods, space 
being given for one-third, one and six-millimeter data. Ke- 
ratometric gives the corneal mal-curvatures and axes. 

Phacometric covers the subjective findings made with trial- 
case lenses. While "U. V." stands for uncorrected vision, and 
"C. V." for corrected. "Amp" for "amplimetric" is the same 
as amplitude of accommodation, only shorter. If it is desired 
to have the blank embrace further tests, then the word peri- 
metric could be used to cover the use of the perimeter, and 



SYSTEMATIC CASE RECORDS 1 47 

under prismometric could be recorded the tendencies toward 
deviation of the extrinsic muscles, called phorometric, while 
under a classification of "tropometric" could be shown the 
actual deviations. Kratometric pertains to strength, and so 
would show duction tests and exercises, all of which could be 
expressed in degrees with the exception of the exercises, and 
the word "over" could call attention to them on the back of the 
blank where space is ample. 

Presbymetric or, literally, old-man measuring, is the same 
as presbyopic, or old-man vision. The prefix ocular, of course, 
connects the eye with all of these measurements. 

"Previous formula" and the rest of the blank needs no 
translation, unless it is to call attention to "segs" for segments, 
in bi-focal work, and to add that under "lenses" can be noted 
the regular, toric, tinted and fused kinds. First quality lenses 
could be termed centex, and second quality could be desig- 
nated as ordigrad. 

For purposes of explanation, let it be supposed that an 
examiner is fallible and does err in judgment, and that a patient 
returns and has a slight change made. This is duly recorded 
on the back of the blank as well as the fact that no charge was 
made for this change. 

In the course of a few months, perhaps, a new "O. D." is 
supplied, which, with its price, is also recorded, and thus the 
blank will last for years, for whenever the patient calls the 
blank can be taken into the examination room and made to 
serve as a complete "book of the play." 

When skiametric examinations are recorded they seldom 
have to be repeated in return cases. It is only the subjective 
tests, and the variations of judgment that, ordinarily, require 
attention. 

Therefore when it is stated that systematic ocular examina- 
tion records are very valuable, from a practical standpoint, this 
statement might go further and class them along with examina- 



I48 RESOURCEFULNESS 

tion rooms and claim both as absolutely essential in this day 
and age, when a pronounced success in optometry is only 
achieved by paying strict attention to every detail of method, 
place and device. 

RESOURCEFULNESS. When to rely on a patient's 
"Yes" or "No," and when not to, requires no small amount 
of knowledge of human nature, as well as ability as a cross- 
questioner. Of course ocular skiametry and other objective 
means place an examiner in a position largely independent of 
a patient's answers or intelligence, yet it is always a source of 
satisfaction to have one method corroborate another, since there 
are many ways in which to be wrong and only one way in 
which to be exactly right. With so-called regular conditions 
skiametrists are likely to have little trouble, but the irregular 
kind frequently call for considerable versatility on the part of 
an examiner in order to extricate himself from a refractive 
corner, so to speak. 

To illustrate this, a case of nystagmus once presented itself 
which had been seen by a half-dozen able specialists. The age 
of the patient was twenty years, and the glasses in use were 
one-diopter concave sphericals for both eyes, which gave an 
acuity of vision equal to about ten two-hundredths. 

The use of the skiascope showed the presence of myopic 
astigmia, with the rule, but the spasmodic action of the muscles 
precluded the ascertaining of the amount. By recourse to the 
keratometer and by engaging the patient in a long conversa- 
tion regarding daily work, in order to quiet the spasm, it be- 
came possible to locate a corneal mal-curvature of about five 
diopters. The use of the mirror again showed the absence of 
any error at right angles, and glasses of four diopters concave 
cylindric at axis 180 after thirty days' use increased vision to 
a little better than twenty one-hundredths. 

When it is borne in mind that this case had been under care- 



MECHANICAL MYDRIASIS 149 

ful observation for twelve years, and that no expense had been 
spared in consulting the most eminent specialists, the joy of 
the patient over the results achieved can readily be imagined. 

A haphazard trial of test lenses might have resulted in a 
clue which could have been followed up satisfactorily, perhaps, 
but this less certain method frequently leads an examiner 
astray through the patient's failure to appreciate and give an 
encouraging answer to a partial correction. 

In the refractive examination of the eyes of children, deaf 
persons, mutes and illiterates, ocular skiametry offers about the 
only reliable means for independently determining the kind and 
strength of proper glasses. 

In this same category might be included those persons who 
are only partially deaf, and who fail to respond to all questions 
asked them. Also those persons who do not speak the same 
language the examiner does, and careless persons who some- 
times prefer to joke and thus unconsciously cause an examiner 
to become careless himself. Then there are the ultra careful 
persons whose answers are about as misleading as though they 
too were careless. 

All of these and many others tend to show the value of 
ocular skiametry, for success must be achieved, no matter what 
the obstacles are, as an examiner can ill afford to endanger his 
reputation through poor work. 

MECHANICAL MYDRIASIS. As pointed out by other 
writers, the production of mydriasis by temporary paralysis 
serves to uncover corneal zones which add much to the con- 
fusion of an operator in making his measurements by the 
shadow test, owing to the refractive variations found from 
center of cornea to circumference of pupil. 

Then, too, habits, which are formed through the efforts 
of nature in trying to adapt herself to the best conditions pos- 
sible, are no doubt responsible for the difference in size of 



I50 MECHANICAL MYDRIASIS 

ocular pupils where the ages and refractive errors of patients 
are the same. Skiametrists will therefore find that mydriasis 
produced by magnifying will give them better results than 
where the constricting muscles of the pupil are paralyzed by 
toxicants, and the reason for this lies in the fact that through 
magnification only that portion of the cornea which is limited to 
the size of the pupil is measured, thus avoiding the peripheral 
zones. 

Enlargement by magnification would seemingly mean an 
increase in size at the expense of definition. Let it be con- 
sidered, then, whether this is really so or not. The word 
"definition," as used in optics, means the power of a lens to 
give an image of anything, or part, so as to clearly distinguish 
it from its surroundings. But this is perhaps misleading, as 
experienced microscopists say that a lens of low power often 
works better than one of high power, because with a low- 
power lens a better general idea may be had of the object, even 
at the expense of size, than if it were viewed through a high- 
power lens. 

It might be reasoned from this, therefore, that it applied to 
the magnifying of the retinal shadow. But here comes the 
examiner's own vision and the law of a five-minute angle gov- 
erning its acuity. If he operated at a much nearer point than 
forty inches, any increase in size of shadow, without correspond- 
ing increase in substance of which it is composed, might 
interfere with the sharpness of demarcation caused by 
magnifying. But many ocular pupils are so small that the 
retinal shadow gives a visual angle of less than one-half, per- 
haps, of what it should at forty inches away, and so, when the 
pupil is magnified to several times its original size, the increase 
in visual angle more than compensates for the decrease in 
sharpness of outline. Hence this explanation to theoretically 
account for that which those who use this method learn to be 
a fact from actual experience. 



MECHANICAL MYDRIASIS 151 

A simple experiment can be tried which will serve to 
emphasize the superiority of this magnification principle. If 
a patient will hold a convex seven-diopter spherical lens two 
inches in front of his eye and let an examiner compare the 
sharpness of outline of the union between the iris and the 
sclerotic from a distance of forty inches away, and then deter- 
mine which one of the patient's two eyes is the easiest to see, 
the magnified or the unmagnified one, the difference will be 
very apparent, and the larger iris will seem to lose little if any 
of its color or intensity on account of magnification. Figs. 

Fig. 59. Fig. 60. 





REGULAR SIZE PUPIL. AREA OF MAGNIFIED PUPIL. 

59 and 60 illustrate the relative size between an average pupil 
and one enlarged three diameters. 

The working distance at which an examiner operates will, 
of course, affect the magnifying power of whatever lenses may 
be used, but as a rule this magnifying principle will be seen to 
take care of itself, for in high degrees of hypermetropia, where 
small pupils are apt to be found, the enlargement caused by 
the lenses in an instrument constructed on mobile principles 
will usually be ample for all practical purposes. 

Where an instrument is not available, a three-cell trial 
frame can sometimes be used to advantage, especially when the 
first and third cells are widely separated. In this case place 



152 MECHANICAL MYDRIASIS 

a minus 20. D. spheric lens in the cell next to the patient, and 
a plus 16. D. spheric lens in the cell next to the examiner, the 
plus 16. D. lens acting as an appreciable magnifier, and its 
distance from the minus 20. D. lens will be sufficient to neu- 
tralize the 4. D. difference in the strength of the lenses. In this 
way small pupils can often be doubled in area, which helps 
greatly when other conditions are poor. 

Another way is to use a strong concave spheric in a regular 
trial frame and then hold a weak convex lens much farther 
away. The manner being the same as the strong convex lens 
is held in practising indirect ophthalmoscopy. 



CHAPTER X. 

Value of Instruments in Practising Optometry. — 
Mobile and Unit Lens Systems. — Various Instru- 
ments Used in Skiametry, With Descriptions of 
Their Mechanical Construction. 

VALUE OF INSTRUMENTS. The value of instruments 
in optometric practice can hardly be overestimated, if accu- 
racy, encouragement and speed are to be considered. For while 
it is true that all optometrists should be so trained as to be 
able to do their work with crude apparatus, it is also true that 
they should be educated in the expert handling of devices which 
tend to make their work more efficient. 

All optometric instruments are at best only tools which 
depend for their usefulness upon the intelligence of those who 
handle them. The confession, therefore, of inability to use 
an instrument is tantamount to a confession of incompetency. 
Some tools and instruments have greater scientific and economic 
value than others have, and it frequently happens that the 
instrument or device whose manipulation is easiest to acquire 
is not always the best one to use. The inexperienced should 
be influenced by the experienced in the selection of their exam- 
ination room armament, provided this experience is adequate 
and its possessor does not belong to that class of examiners 
who get into ruts and are incapable of extricating themselves, 
no matter what the true value of the optometric inducement 
may be. 

In the selection of instruments there is one point which 
usually commends itself to those who have had opportunities 
of using various kinds, and that is the superiority of mobile 



154 



MOBILE LENS ACTION 



action over the unit action of lenses. This so-called "unit" 
in the ophthalmic lenses in general use to-day is termed "one 
diopter," but in reality the unit comes nearer to being an eighth 
of a diopter, as lenses are now employed, these small quan- 
tities acting as steps whereby the accommodation of an eye is 
compelled to jump from one adjustment to another. 

To overcome this jumping principle in the measuring of 
convergence the "Risley" mobile prism was invented. This 
prism arrangement serves to change these abrupt degree- jumps 
into a sort of sliding motion, thereby permitting a gradual in- 
crease or decrease in the light deviation, and resembling the 
action of a wedge while being made to lift a weight. 



Fig. 6i. 



+4D. 




Xm$ fostfc 



MB 

REFRACTION BY LENSES PLACED CLOSE TOGETHER. 



MOBILE LENS ACTION. With both cylindric and 
spheric lenses this sliding principle can be imitated. Thus two 
convex lenses of four diopters each when placed close together 
on their optical axes give a combined refraction of eight diop- 
ters, with a focal power equal to five inches. Separate these 
two lenses two inches and their combined action will represent 
nine diopters of refraction, having a focal distance of four and 
a half inches. The increasing or decreasing of the distance 
between any series of lenses on their optical axes serves to 
produce a mobile effect similar to the action of the crystalline 
lens in a living eye, thus enabling accommodation to be given 



MOBILE LENS ACTION 



155 



the same character of assistance as that accorded to convergence 
by a mobile prism. Figs. 61 and 62 will make this point plainer. 
That this mobile action is a valuable factor in dealing with 
stubborn cases of spasm is not difficult to perceive, any more 
than it is difficult to note the fact that the raising or lowering 
of a heavy safe by sliding on a plane is easier than it would 
be by using a series of steps. The evenness of the sliding mo- 
tion serves to induce an accuracy of action that can hardly be 
imitated by a motion which might, perhaps, be best described 
as by jumps or by leaps. 



Fig. 62. 



+4D. 




^fe/nthfocuc. 



+4D 
REFRACTION BY LENSES WHEN SEPARATED. 



An eye is often considered as having an error equal to one 
and three-quarters diopters, whereas, the true error may really 
be one and five-eighths diopters or one and seven-eighths, the 
one and three-quarters merely indicating an approximate cor- 
rection. In many cases this would undoubtedly be near enough, 
but in others a knowledge of the exact refraction is often of 
importance. Therefore, where a mobile lens system is employed 
there is a greater tendency toward precision than where lens 
units are relied upon. 

Then too, the relaxation of accommodation will be found 
much easier with a mobile lens system than it will be with a 
unit system, for in reality the mobile practically amounts to 



156 



UNIT LENS ACTION 



the measuring of a living eye by means of an artificial one 
possessing similar refractive powers of adjustment. 

The invention of a single mobile lens capable of adaptation 
to the needs of mankind would undoubtedly prove a great boon, 
but until such an invention appears reliance will have to be 
placed upon a series of lenses arranged for the accomplishment 
of similar purposes. 

Fig. 63. 




KING S BINOCULAR HAND TRIAL SET. 



UNIT LENS ACTION. There is one form of the step- 
like arrangement of lenses that will be found exceedingly 
valuable in corroborative work, and that is in the old-fashioned 
metal or hard rubber device illustrated by Fig. 63. 



VARIOUS INSTRUMENTS USED IN SKIAMETRY 1 57 

There should be four pairs of plus and minus, half and quar- 
ter-diopter spheric lenses mounted so they can be used in either 
a monocular or binocular manner. This device can be employed 
both objectively and subjectively, either for near or distant tests, 
and can be held by the examiner or by the patient. Its con- 
venience in the addition or removal of weak lens power serves 
to determine accommodative action, and frequently gives that 
slight fog to vision which enables both patient and examiner to 
easily differentiate small quantities of astigmia. 

In the final study of a case, after the correcting lenses are in 
position, an examiner will find the use of lenses mounted in 
pairs, such as shown in Fig. 63, and placed in front of the trial 
frame, to be an easy way of obtaining those little niceties in 
refractive adjustment which contribute so much toward the com- 
plete visual comfort and satisfaction of a patient, and which also 
make one examiner's work just a little better than another's. 

VARIOUS INSTRUMENTS USED IN SKIAMETRY. 
Skiametry is somewhat similar to indirect ophthalmoscopy, inas- 
much as an operator is obliged to do several things at one time. 
After shadow testing had been improved and brought to a state 
approaching practical usefulness by men like Cuignet, Parent, 
and others, it was found that its application entailed such fre- 
quent changing of lenses as to discourage its common use. 

The first effort of importance along the line of labor-saving 
devices for skiametric work was the lens rack, or hand ski- 
ameter, to which the name of Wurdemann is frequently at- 
tached, although its invention is claimed by a large number of 
others. 

Fig. 64 illustrates the constructive principle of this instru- 
ment and, as will be seen, it consists of a series of plus and 
minus spheric lenses mounted in such a manner as to permit of 
the patient holding them before his eyes and moving the lenses 
from one strength to another, at the request of the examiner. 



I58 VARIOUS INSTRUMENTS USED IN SKIAMETRY 

Inasmuch as it proves a saving of time and labor, this device 
is a decided improvement over the use of single lenses placed 
in a trial frame. Among the drawbacks to its use, however, will 
be found the stupidity and carelessness of patients, who fre- 
quently permit the lenses to rest at angles which interfere with 
their correct refraction and thus necessitate a constant readjust- 
ment of the rack by the examiner. Then, too, owing to this 
same stupidity and carelessness, a patient will often allow the 
lenses to come in contact with the skin on the forehead, eyelids 
or cheeks, and thereby soil the lenses so they become unfit for 
use until after they have been cleaned. 

Fig. 64. 




SKIAMETRIC LENS RACK OF WURDEMANN. 

Quite a number of modifications of the Wiirdemann prin- 
ciple have been produced, but the drawbacks just mentioned 
seem common to them all. 

The Crain disc and the Standart annular ring of lenses are 
both popular: the first named being on a stand for use on a 
table, while the last named is held by a wall bracket. Fig. 65 
shows the large disc of lenses used in the Crain device. 

The lenses of the disc can be either spheric or cylindric as the 
examiner chooses. The disc can also be revolved by the exam- 
iner or by the patient at the former's request. These discs, or 
batteries of lenses, are something of an improvement on the 
hand rack of Wiirdemann, inasmuch as they hold the lenses in 
such a position as to permit of no material twisting or dis- 
turbance to their principal axes. The reliance on the patient to 



VARIOUS INSTRUMENTS USED IN SKIAMETRY 



159 



turn the discs and the necessity for troublesome adjustments as 
to height, together with the annoyances incident to keeping the 
head of the patient so situated that the eyes will always be in 
proper position, constitute some of the reasons why these de- 
vices have not been in greater demand. 

The Standart "Umbrameter" is an instrument thoroughly 
vouched for by its inventor, who is one of the foremost optom- 
etrists of America ; Fig. 66 shows its general construction. 

Fig. 65. 




LENS DISC USED BY CRAIN AND OTHERS. 



The makers of this device tell of its merits in the following 
words : 

"Time is a great element with a busy refractionist. A pa- 
tient in the chair and a half dozen waiting means that unless 
the operator is rapid in his work, some of the waiting ones 
will get tired and go out. 

"The Standart Umbrameter is designed to save time, to 
contribute to accuracy in results and impress the client with the 
skill and efficient equipment of the up-to-date refractionist. 



i6o 



VARIOUS INSTRUMENTS USED IN SKIAMETRY 



"Combining accurately all spheres from one-quarter to six 
and one-half dioptrics by quarters, and from six and one-half 
to nine dioptrics by halves, and all cylinders from one-quarter 
dioptric to seven and three-quarters dioptric by quarter diop- 
trics, set at any axis, with their manipulation easily accom- 
plished at one meter distant, makes this instrument the most 
perfect adjunct of the retinoscope ever devised. 

Fig. 66. 




STANDART S UMBRAMETER. 



"A little practice will make it an indispensable addition to 
the instrument avium of the operating room. It will save its 
cost in a short time by increasing sales during the busy hours 
of the day, rendering changes less liable to be necessary and 
saving that valuable element — time. 

"The operation is simple: Loosen the thumb screws on rod 
pinions and grasp the hanging upright bar with the right 
hand, then with the left hand turn geared lens ring around 
until o is shown in the number aperture on lower part of the 
frame; this is the zero point. 



VARIOUS INSTRUMENTS USED IN SKIAMETRY 1 01 

"Direct the patient to assume an easy position and to look 
towards some object 15 or 20 feet away pinned upon the wall 
so that the line of patient's vision will just come over the top 
of operator's head while seated 40 inches away facing patient. 

"Adjust the instrument up or down, turning it sideways and 
tipping the annular rings up or down to bring it to the proper 
position before the patient's eye. 

"From the trial set slip under springs on the back of the 
eye hole a spherical convex lens of sufficient power to create 
a positive pseudo myopia. If the case is one of known myopia 
of over 1. 00 D., leave the supplemental lens out, or if it is 
discovered after a little examination that it is a case of true 
myopia or myopic astigmatism, then this supplemental lens may 
be removed, if desired. 

"This is the fogging system applied to skiascopy, the most 
accurate yet discovered. There is a diversity of opinion as to 
the relative value of piano or concave mirrors. We suggest for 
use the concave of about 1 dioptric curve and with a hole not 
more than two millimeters in diameter. 

"Seated on a revolving stool that may be raised or lowered 
one meter (40 inches), from patient, the length of the rods, 
and a light, preferably an Argand burner with a flame about 1 
to iy 2 inches high, over the head of the patient and slightly 
back, direct the patient to look over the top of your head at 
some object on the wall. 

"In the right hand is held the mirror and in the left one of 
the rod handles, the other rod being suspended therefrom by 
an S link. Secure a clear fundus reflex through the aperture 
provided for the patient to look through, and then turn spheres 
until one medium stands still. If there is then astigmatism 
present, calculate the axis, then adjust the annular ring con- 
taining cylinders so that the mark on scale shows the meridian 
determined and then proceed as before until that meridian is 
neutralized. Should the astigmatism appear in the vertical, or 



1 62 



VARIOUS INSTRUMENTS USED IN SKIAMETRY 



its approximations, use the white scale revolving the lenses 
downward bringing the cyls, setting vertically on the instrument, 
downward. Should the astigmatism appear in the horizontal, 
or its approximations, then use the red scale revolving lenses 
set in the instrument horizontally upward into position. 

Fig. 67. 




THE MERIDEN OCULOMETROSCOPE. 



"The ring containing spheres may be turned down or up 
on its axis to suit convenience and comfort of the patient with- 
out affecting the axis of the cylinders." 

The "Oculometroscope" made by the Meriden Optical Man- 
ufacturing Company, is shown in Fig. 67. 

This is perhaps the latest form of disc instruments. It 
carries its own lamp and has a turning rod attached to each 
disc whereby an examiner is enabled to change lenses without 



VARIOUS INSTRUMENTS USED IN SKIAMETRY 163 

altering his position when operating at a distance of forty or 
more inches away. 

The manufacturers of this instrument set forth its use, 
as follows : 

"With this instrument you can measure the far point, near 
point, amplitude of accommodation, hypermetropia, myopia, 
presbyopia and astigmatism. Also the muscular insufficiencies 
by using a prism from your trial case. It can be used for 
both objective and subjective tests. 

"The Oculometroscope is a great time saver in using the 
fogging system, and in retinoscopy by the static, dynamic or 
fogging methods. With it you can locate the axis for cylin- 
ders without the use of a chart. 

"As a time saver in retinoscopy this instrument is unex- 
celled. You can save the time usually lost in changing lenses 
in trial frame and in finding the reflexes, time after time, and 
also avoid the danger of small errors from not getting the one 
meter distance every time. 

"Seat the patient comfortably before the instrument with 
chin in the rest and eyes looking through the open disc. Care 
must be taken to have the centers of the discs properly ad- 
justed for the patient's p. d. Have the patient look into the 
distance, relaxing the eye as much as possible. Rotate the 
lens discs by rod until plus i.oo appears in the indicators. 

"Turn on the light, and with the plane mirror at the end of 
the graduated rod (which is exactly one metre from the 
patient's eyes) proceed to examine the eyes with the mirror. 
You do not have to move mirror from position to change 
lenses in front of patient's eyes, and you are always sure of 
maintaining a one-metre distance. 

"This means a great saving of time usually lost in changing 
lenses in trial frame, and finding reflex, time after time, also 
lessens the danger of small errors from not getting the one- 
metre distance every time." 



i^^M^n 



164 VARIOUS INSTRUMENTS USED IN SKIAMETRY 

The latest model of what is known as the "Geneva Retino- 
scope," manufactured by the Geneva Optical Co., of Chicago, 
is shown in Fig. 68. 

Fig. 68. 




THE GENEVA RETINOSCOPE. 

The makers put forth the following claims of merit for 
this instrument, which also combines an indirect ophthalmo- 
scopic adjustment. 

"This instrument makes use of the direct method of retinos- 
copy, the most valuable of methods for testing the refraction of 
the eye, because (1) it is an objective test and requires no 
catechism of the patient, and (2) because of its wonderful 



VARIOUS INSTRUMENTS USED IN SKIAMETRY 165 

exactness. But the instrument offers special advantages to the 
retinoscopist above those possibly obtainable by the hand method. 
These are chiefly as follows : 

"ist. The instrument introduces no new principle, but 
simplifies the general method of skiascopy as practiced in the 
dark room with a plane mirror. The same rules that govern 
in the hand method govern also in the use of the instrument, 
and those who are experienced in the test have nothing to 
unlearn. 

"2d. The instrument may be operated in a light, airy 
room or the regular office for refraction work. This enables 
the operator to combine with it the fogging method for re- 
ducing ciliary spasm. This combination is impossible in dark 
room skiascopy, for darkening the room to brighten the reflex 
obscures the distant object by which the accommodation is 
properly fogged. 

"3d. The mirror is so fixed that it may be tilted true to 
any given meridian and so arranged that it may be rotated to 
any meridian and remain stationary in that meridian as long as 
desired. This gives a far greater degree of accuracy in locat- 
ing the two principal meridians in an astigmatic eye than is 
possible with an ordinary hand retinoscope, as used in the 
method hitherto practiced. 

"4th. The light, mirror, patient's eye and observer's eye 
are always in their exact relative positions, and there is no time 
wasted, therefore, in finding the patient's eye or keeping it in 
view when found. Moreover, having the distances all fixed 
once and for all, the operator does not need to keep them 
perpetually in mind or think of them at all. He can devote 
his whole attention to watching the movements of the reflex 
and shadow and operating the lens discs to get the result he 
requires. 



l66 VARIOUS INSTRUMENTS USED IN SKIAMETRY 

"5th. There are no deductions or additions to be made 
when the right lens is found, for the distances are all neu- 
tralized to infinity with plus lenses fixed in the instrument. 
The point of reversal of an emmetropic observed eye is always 
about one inch back of the mirror, or where the cornea of the 
observer's eye will be when the best view of the pupil is 
obtained. 

"6th. There are arranged in the instrument two large ro- 
tating discs in which are fixed batteries of plus and minus 
lenses. These discs may be so rotated as to bring any desired 
plus or minus lens before the patient's eye. This obviates the 
necessity of reaching forward to change the lenses from the 
trial case during the examination — one of the most inconvenient 
features of open retinoscopy, as generally practiced. 

"7th. The lights used may be changed in one minute from 
oil to gas or electric, as they are interchangeable." 

The De Zeng Combined Optometer, Phorometer and Ski- 
ameter, manufactured by the De Zeng-Standard Co., Camden, 
N. J., is another late invention designed for use in both objec- 
tive and subjective optometry, also for muscle measuring and 
exercising as well. 

Fig. 69 shows the general appearance of the head of this 
instrument, which can be mounted either on a bracket or on a 
stand. 

The manufacturers set forth the merits of this compre- 
hensive device in the following claims: 

"This new instrument is a perfect combination of our well 
known Phoro-Optometer and a binocular quadruple series of 
plus and minus spherical lenses mounted in light disk form. 
It is exceedingly compact and complete, is unusually light, well 
finished and is the best all around instrument ever offered for 
Objective and Subjective Refraction and Muscle Work. 

"The lenses are all one inch in diameter, are accurately 



VARIOUS INSTRUMENTS USED IN SKIAMETRY 



167 



ground and centered, and may be brought into operative posi- 
tion separately or in combination as desired. The first disk 
facing the operator contains o, .25, .50. .75, 1.00, 1.25, 1.50 
and 1.75 in plus spheres; the second disk carries the same 
numbers in minus spheres, the third disk holds the first series 
of auxiliary numbers, and by a partial rotation outward from 
zero, 2.00, 4.00 and 6.00 in plus are obtained, while an inward 
movement from zero gives 2.00, 4.00, 6.00 and 8.00 in the 

Fig. 69. 




DE ZENG S OPTOMETER, PHOROMETER AND SKIAMETER. 



minus. The fourth disk contains the second series of auxiliary 
numbers, and by a partial rotation of the disk downward from 
the horizontal position of the Controlling Arm, which is lo- 
cated at zero, plus .12, 8.00 and 1.50 are obtained, while an 
upward movement from zero gives minus .12, 10.00 and blank. 
The plus 1.50 lens is for use in Retinoscopy at a 26-inch work- 
ing distance, which is within arm's reach of the Instrument. 
By combining the contents of the first disk with the positive 
auxiliary numbers in the third and fourth disks, all of the 



1 68 VARIOUS INSTRUMENTS USED IN SKIAMETRY 

positive equivalents from .12 to 7.87 inclusive are obtainable in 
eighths, and from .25 to 15.75 inclusive in quarters. The 
negative equivalents are likewise obtained by employing the 
second disk in conjunction with the minus auxiliaries carried 
by the third and fourth disks, but in the minus numbers the 
range is extended to 9.87 in eighths and to 19.75 in quarters." 

With the exception of the author's instrument which, as 
will presently be seen, is a radical departure in almost every 
way from those just referred to, this completes the list, although 
there are still quite a number of other instruments which 
embrace the principles here shown. 

Jackson in his valuable book on Skiascopy, in speaking 
of the use of disc lenses (page 109) says: "But even in this 
case, the fact that there is a complete break between the 
appearances represented by one lens, and the appearances 
present by the use of the lens next stronger or weaker, makes 
the information obtained less valuable and satisfactory than 
that derived from the movement of the surgeon's eye from 
one position to another, which allows him to watch the dif- 
ferent appearances of light and shade as they pass gradually 
into each other'' This "movement of the surgeon's eye" to 
which he refers has since been practically duplicated by mak- 
ing the lens action mobile instead of fixed, thus securing 
superior results with less effort. 

From the instrument of Crain to that of the Geneva it 
may be observed that the proper adjustment of the patient's 
head by means of chin rests, etc., is an important item, and, 
with the exception of the oculometroscope type of instrument 
they all require separate adjustment for each eye. Besides, 
not one of them is arranged for magnifying the patient's pupil, 
no matter how small it may be nor how great the difficulty of 
accurately noting the action of its shadow. 

All of the disc type of instruments are designed to work 
at one fixed distance, no latitude being allowed unless they 



author's skiameter 169 

are operated in an awkward manner, and this of course limits 
their use to the static method only, barring out the dynamic, 
which of the two is really the more valuable. Therefore, all 
monocular testing instruments are of little service in thorough 
skiametric work. 

Wiedemann's device is, like the use of trial lenses, most 
excellent in theory, but in practice its shortcomings seem to 
be many. In the practical workings of all disc devices their 
use usually proves of considerable assistance to an examiner, 
especially when the disc can be controlled by rods, but all disc 
instruments, it is feared, will eventually be relegated to the 
company of the many other optometric devices which have been 
weighed in the balance and found wanting. However, it is 
for others to judge of this after they have informed themselves 
regarding the advantages gained by the use of the next instru- 
ment to which attention is here called. 

THE AUTHOR'S SKIAMETER. This little device, 
among its other features, was designed to accomplish a pur- 
pose similar to that of the various disc contrivances in over- 
coming the necessity for having examiners change position 
every time a lens needed changing. Like Wiedemann's device, 
too, it was designed as a hand instrument, so as to make the 
adjustments rapid and easy, but unlike Wiedemann's rack, it 
was arranged to be so placed that its position should be as 
secure as that of a trial frame. 

Enlargement of ocular pupils was sought for and achieved, 
together with mobile lens action. Variety in methods of oper- 
ating was not so much a first consideration as it was an after- 
thought. The construction of the instrument, however, needed 
very little alteration after dynamic skiametry was developed, 
although the addition of this method to the value of the instru- 
ment has been found too great to be estimated by figures. 

Binocular action was also an original feature ; then sim- 



■HH 



170 



AUTHORS SKIAMETER 



plicity; not only simplicity of construction and action, but 
simplicity of operation. Fig. 70 shows the mechanical arrange- 
ment of the instrument and the manner of the adjustment of 
its lens system. 

Two convex and two concave cylindric lenses of seven 
diopters each are mounted in cells A and B, and A and B 
prime, with their axes at right angles to each other, each lens 
being slightly inclined from the perpendicular on its meridional 

Fig. 70. 




CONSTRUCTIVE PRINCIPLE OF AUTHOR S SKIAMETER. 



axis. The two concave lenses are stationary while the two 
convex ones are made movable. The cells of the latter slide 
on rod H, being controlled by a doubled cord C, D, thirty-six 
inches in length, this cord passing over pulley F. The cord's 
length being always the same, an operator has merely to turn 
his hand at the wrist in order to obtain full control of the 
refractive changes of the instrument. 

In the use of convex cylindric lenses it was found that 
by placing each cell on a sliding block, such as shown by K 
and E, and by then using a hook the operator could unfasten 



AUTHOR S SKIAMETER 171 

them while working at a distance by merely moving his hand 
a few inches to one side. The cylindric lenses used in this 
way could also be made to serve a double purpose; for when 
used together they acted as a single spheric lens does, but when 
used singly, or unlocked, they acted as simple cylinders. 

Another valuable principle was also discovered and made 
use of. It was found that as the plus cylinders, A and B 
prime, were moved away from the minus cylinders, A and B, 

Fig. 71. 




AUTHOR S SKIAMETER, WITHOUT BASE. 

any object, such as a patient's eye, when placed close up to 
the concave lenses, would be magnified by the convex ones, just 
as though a plain seven-diopter convex spheric lens had been 
used, this magnification taking place without causing the least 
interference in the refraction of the four lenses while they were 
being used as a lens series to produce mobility of action. 

Other attachments comprise a self-adjusting brow rest to 
give the instrument stability, a handle, a base and a means for 
separating the two tubes. The large holes now in the top of 



^^^m^^^a^mm 



172 author's skiameter 

the tubes of the latest model instrument facilitate the cleaning 
of the lenses, whose cells are all attached to blocks on the slide 
rods. The minus cylindric lenses are secured in position by 
a set screw in the block holding cell B. 

Fig. 71 shows the instrument complete, with its auxiliary 
lens disc containing three sphericals, i. e. } — 1. — 3. and — 
6. D., to be used in converting the instrument from the static 
to the dynamic method, also for changing the total refraction 
from plus to minus, as occasion demands. 



CHAPTER XL 

Questions and Answers Pertaining to Static and Dy- 
namic Skiametry and Correlated Subjects, With 
Pertinent Remarks Emphasizing the Salient Points 
Involved. 

There is perhaps no better way in which to fixedly impress 
upon the mind of the student the underlying principles gov- 
erning ocular skiametry than to require him to answer a series 
of questions embracing the salient points involved in the sub- 
ject. The remarks following each answer given in this chapter, 
though sometimes a repetition of matter contained in previous 
chapters, will also serve to emphasize the principal points 
involved. But to avoid creating any wrong impressions it may 
be well to preface these questions and answers by calling atten- 
tion once more to the fact that the subjects are here treated 
in a purely theoretic manner. For instance : If by dynamic ski- 
ametry the intrinsic and extrinsic muscles are not in a "i to 3" 
relationship then the refractive findings will not be the same as 
though these muscles maintained this so-called "standard" 
harmony. 

One of the greatest points of merit of skiametry is that it 
always tells the exact truth, even though examiners cannot 
invariably interpret this aright, but when a shadow moves 
either with or against a mirror's movement it indicates that the 
conjugate focus of the emerging ray is either posterior or 
anterior to the examiner's position of observation. 

The cause influencing focal length of the emerging rays is 
quite a different question from that of reading the action of 
the shadow, for what is known by the names, latent hyperopia 



174 QUESTIONS, ANSWERS AND REMARKS 

and sub-normal presbyopia, may be merely a changed relation- 
ship between accommodation and convergence that is peculiar 
to the case under examination. 

Skiametry merely determines the state of the refraction at 
any given point, the same as phorometry can be made to show 
the co-ordination of the two eyes for any point of convergence. 
With skiametry, however, the examiner is largely independent 
of the patient's reliability, whereas, with phorometry it depends 
entirely upon a patient's replies to set questions which thus 
form a very uncertain quantity. 

In the questions following No. 24 it will be noted that 
-fixation is never placed nearer the patient than that of observa- 
tion. Theoretically it ought not to make any difference what 
relationship these two factors bear to one another, but in prac- 
tical application it will be found .that attempted fixation for a 
point inside of the patient's punctum proximum will be pro- 
ductive of very uncertain results until the correction nears the 
point where fixation and observation become equal. 

Where fixation is beyond the point of observation then more 
reliable findings are obtained, but for extreme accuracy of 
measurement it is necessary that fixation and observation should 
be the same, lenses being used for altering the focal length of 
the emergent rays Avhile the examiner remains in a fixed po- 
sition. 

Familiarity with both ray-value and lens-value methods 
enable an examiner to cover a much wider range of measure- 
ments, also to work with greater speed and to secure data that 
materially aids in the correct formation of that judgment which 
predetermines success. 

Question No. i. Reduce and transpose the following 
formula : 

— 0.50 D. S. C + 1. D. C. axis 15 C + 0.25 D. S. 
C — 0.75 D. C. axis 105. 



QUESTIONS, ANSWERS AND REMARKS 1 75 

Write the answer three ways. 

Answer No. i. 

+ 0.75 D. C. O — 1. D. C. axis 105. 
+ 0.75 D. S. C — i-75 I>. C. axis 105. 
— 1. D. S, C + 1.75 D. C. axis 15. 

Remarks, No. i. The reduction and transposition of lenses 
belongs properly under theoretic optics, but its relation to ski- 
ametry is so pronounced that unless a student makes himself 
master of at least one reliable system his progress in shadow- 
testing will, indeed, be difficult. 

The author's system of converting all lens values into 
cylindric equivalents and then reconstructing these into desired 
combinations will give the best forms for the purposes needed 
and will be found one of the simplest ways of dealing with this 
complex problem. 

By "best forms," it may be added, that in this age of atten- 
tion to details, it frequently happens that an examiner desires 
to write his formula so as to obtain a meniscus effect in the 
completed lens, or else he may prefer to so combine his bi-focals 
that the segment will always be on the inside of the lens. The 
form of reduction and transposition described herein makes 
this possible, hence its importance to the student. 



Question No. 2. With a schematic eye set at emmetropia 
and having a + 0.75 D. S. lens before it, how many inches 
away will the skiametric reversal point be ? 

Answer No. 2. Fifty-three inches. 

Remarks, No. 2. This is a case of simple artificial myopia. 
In the living eye, however, if the patient had unconsciously 
looked at any object within infinity, say at fifteen feet away, 
then accommodative myopia would be a factor, and the total 
myopia present would be 1. D., making the point of reversal 
at forty inches instead of at fifty-three. 



I76 QUESTIONS, ANSWERS AND REMARKS 

Twenty feet is usually considered as infinity in practical 
optometry, but for real accurate measurements this classification 
will be found untrustworthy, as a lens of 0.12 D. has a focal 
length of over twenty-six feet, and in these days formulas 
calling for 0.12 D. lens-power are not uncommon. 



Question No. 3. With a schematic eye set for 1. D. of 
myopia, and having a lens — 1. D. C. axis 90 before it, how 
far away will the skiametric point of reversal be in the vertical 
meridian ? 

Answer No. 3. Forty inches. 

Remarks, No. 3. It is well known that in an emmetropic 
eye a plus lens held before it creates myopia. If the lens is 
minus, however, then the artificial error is hyperopia. And if 
the lenses used are spherics then the error is in all meridians, 
but if cylindrics are used then the error is only in the meridian 
at right angles to the axis of the lens employed. 

In question No. 3 the required myopia for forty inches 
working distance is obtained by slightly lengthening the sche- 
matic eye, and thus what might be considered as true myopia 
is a factor. 

The use of a — 1. D. C. lens, axis vertical, would serve to 
neutralize this true myopia in the horizontal meridian, thereby 
causing the rays to emerge parallel, but the rays in the vertical, 
not having been interfered with, continue to converge to a point 
I. D., or forty inches away. 



Question No. 4. With a schematic eye set for 1. D. of 
myopia, what lenses should be added to artificially produce a 
mixed astigmatic error equal to — 1.25 D. S. C + 2. D. C. 

axis 45 ? 



questions, answers and remarks 1 77 

Answer No. 4. 

+ 1.25 D. S. C — 2. D. C. axis 45 or — 0.75 D. S. 
C + 2. D. C. axis 135. 

Remarks, No. 4. As myopia is produced with a plus lens 
and hyperopia with a minus one then all that is required in the 
above case is to use lenses of the same strength but opposite 
kind, and if for any reason these lenses are not available then 
the second formula, given in the answer, can be made use of, 
this being obtained by transposition. 

In a living eye the artificial, or "working," myopia would 
have to be produced by a + 1. D. S. lens, and then this quan- 
tity would have to be taken into consideration in the final 
analysis. But with schematic eyes the artificial myopia can be 
made into true myopia by simple adjustment in length, so for 
purpose of practice work the question of "working quantity" 
can be temporarily eliminated. 



Question No. 5. What is the difference between tonic and 
clonic spasm? 

Answer No. 5. Tonic spasm is a persistent, involuntary 
contraction of a muscle, whereas clonic spasm is an intermittent 
contraction. 

Remarks, No. 5. It would seem to matter very little to an 
examiner what the character of the spasm was that confronted 
him if it was not for the theoretic side of his work. Tonic 
spasms are met most frequently in hyperopic cases, and clonic 
in myopic ones, habit forming a marked factor. These two 
kinds of spasms, then, are probably responsible for the frequent 
overcorrections found in myopia and for the undercorrections 
found in hyperopia, therefore all examiners should adopt such 
methods as will eliminate the influence of these uncertain 
factors. 



I78 QUESTIONS, ANSWERS AND REMARKS 

Question No. 6. How many degrees of convergence does 
a hypermetrope of 2. D. suppress when his accommodation is 
adjusted for infinity ? 

Answer No. 6. About six degrees. 

Remarks, No. 6. For ease of comprehension the "1 to 3" 
relationship between accommodation and convergence will per- 
haps be found better than where meter angles are used. Thus, 
in question No. 6, it is easy to understand that if 2. D. of 
accommodation is used to overcome the hypermetropia, then 
2 times 3 degrees equals 6, and if binocular parallelism is neces- 
sary of the correct registration of rays of light from infinity, 
then suppression of convergence must be made. The intrinsic 
muscles in this case dictating to the extrinsic ones. 



Question No. 7. How many diopters of accommodation 
does a myope of 2. D. exert when he converges to a point call- 
ing for 9 degrees? 

Answer No. 7. One diopter. 

Remarks, No. 7. The reasoning is simple ; if 9 degrees of 
convergence call for 3. D. of accommodation and 2. D. of 
myopia neutralizes 2. D. of accommodation, then the difference 
between the accommodation that ought to be used and the 
accommodation that is not used gives the amount of accommo- 
dation that is used. 

If A owes B $3, and B owes C $2, then if C owes A $2, 
there is a chance to settle these differences by the payment of 
only $1, all of which can be worked out by a little figuring. 



Question No. 8. What is the difference between static 
and dynamic skiametry? 

Answer No. 8. "Static" skiametry is where fixation is at 
infinity, while "dynamic" skiametry is where fixation is within 
infinity. 



QUESTIONS, ANSWERS AND REMARKS 1 79 

Remarks, No. 8. The above definition is probably as short 
as a technical one can be given. This question is asked so 
often, however, that perhaps it ought to be answered in a num- 
ber of ways. 

Static skiametry is where accommodation is supposed to be 
relaxed. Dynamic skiametry is where it is supposed to be 
exerted. 

The word "supposed" is used because in static skiametry 
accommodation is rarely ever fully relaxed, and in dynamic 
skiametry accommodation is rarely ever fully exerted, spasm 
in relaxation and lag in exertion, are both to be reckoned with. 

Static skiametry can be used for determining the patient's 
easy adjustment of his ocular muscles for distance, while 
dynamic skiametry can be used for determining the easy ad- 
justment of the ocular muscles for reading or near work. 



Question No. 9. By static skiametry with fixation at 
infinity and observation at 26 inches, what should be the 
strength of the lens used to create the working, or artificial, 
myopia ? 

Answer No. 9. + 1.50 D. S. 

Remarks, No. 9. At whatever distance an examiner op- 
erates in the static method he must be careful to know its exact 
dioptric value. Thus, if his observation is made at 10 inches 
he must have an artificial myopia of 4. D. If at 20 inches 
then 2. D., and so on. 

If, however, he uses a 2. D. working quantity and care- 
lessly makes his observation from a point 18 inches from his 
patient, then his findings will show an overcorrection of 0.25 D., 
for 18 inches calls for a lens quantity of + 2.25 D. 



Question No. 10. By static skiametry if a + 2.25 D. S. 



l8o QUESTIONS, ANSWERS AND REMARKS 

lens in front of an eye causes reversal in all meridians at 40 
inches observation, what is the apparent error? 

Answer No. 10. 1.25 D. of hyperopia. 

Remarks, No. 10. The word "apparent" is used here ad- 
visedly. A static examination made at 40 inches, or any other 
distance, gives the exact refraction under the existing condi- 
tions, but often these "conditions" are based on an adjustment 
between accommodation and convergence which gives a re- 
fractive finding that is not in harmony with the one found 
for reading distance, therefore it will be seen that accuracy 
in judgment calls for measurements made at various distances. 



Question No. 11. By static skiametry, if a patient has 1. D. 
of hyperopia, where will the point of reversal be in all meridians 
when a + 2.75 D. S. lens is used? 

Answer No. 11. At twenty-two inches. 

Remarks, No. 11. In this case the patient's error neu- 
tralizes, or absorbs, 1. D. S. of the artificial myopia, leaving only 
1.75 D. remaining. 

If the patient's error had been myopic, instead of hyperopic, 
'then the total would have been an increase instead of a 
decrease. 

Careful attention must always be given to the kind of 
myopia present, whether it is true or artificial, and then to keep 
in mind that hyperopia neutralizes myopia, and that myopia 
does the same for hyperopia. 



Question No. 12. By static skiametry without any lenses 
on, if reversal is found in all meridians at 13 inches from pa- 
tient's eyes, what is the error? 

Answer No. 12. 3. D. of myopia. 



QUESTIONS, ANSWERS AND REMARKS l8l 

Remarks, No. 12. It will be seen from the above that one 
of the easiest ways to estimate myopia is by a tape measure in 
place of lenses. In hyperopia, however, the use of lenses is 
imperative, for it will be borne in mind that myopia of some 
kind, true, artificial or accommodative, must be present in order 
to make use of the principles of shadow-testing. 



Question No. 13. By static skiametry if a patient has 
1. D. of myopic astigmia in the vertical meridian, how many 
inches away will the point of reversal be in the horizontal 
meridian when he uses a + 1. D. S. lens? 

Answer No. 13. Forty inches. 

Remarks, No. 13. If the student will keep in mind that all 
eyes must be measured in two meridians, that of greatest and 
least refraction, the above will resolve itself into a simple case 
of reduction. The two chief axes are 90 and 180, and the 
-f i.D. S. lens creates artificial myopia of 1. D. The reduc- 
tion then is as follows : 

Axis 90 

+ 1. 



Axis 180 

+ 1. 

+ 1. 



+ 1. + 2. 

. The refraction in the vertical meridian shows a reversal 
point at 20 inches. 

The student must not forget that minus neutralizes plus, 
and that myopia therefore indicates a plus condition, because 
it takes minus lenses to counteract it. 



Question No. 14. By static skiametry at 40 inches obser- 
vation, ii a + i.D. lens causes reversal in the vertical meridian 



^^■^■^■^^■H 



l82 QUESTIONS, ANSWERS AND REMARKS 

and it takes a + 2. D. to cause reversal in the horizontal, what 
is the error? 

Answer No. 14. .+ 1. D. C. axis 90. 

Remarks, No. 14. This is a case for transposition. 
Axis 90 Axis 180 

+ 2. + 1. 

and this equals -f- 1. D. S. C + 1. D. C. axis 90. Adding 
— 1. D. S. for the neutralization of the artificial myopia, the 
error then becomes + 1. D. of hyperopic astigmia in the hori- 
zontal meridian, with the axis in the vertical. 

Students must be careful not to get axis and error confused, 
for an eye that measures 52. D. in the vertical meridian and 
51. D. in the horizontal could be made 52. D. in all meridians 
by the use of a cylindric lens of + I- D- axis vertical. 



Question No. 15, By static skiametry, if a patient has 
compound hyperopic astigmia that can be neutralized with a 
lens of + 1. D. S. 3 + 1. D. C. axis 90, where will the points 
of reversal be in the horizontal and vertical meridians when he 
uses a + 3. D. S. lens? 

Answer No. 15. Forty inches in the horizontal and twenty 
inches in the vertical. 

Remarks, No. 15. This is another case of reduction. The 
student remembering that if myopia is a plus condition then 
hyperopia must be a minus one, and on this basis the reduction 
would be expressed as follows : 

Axis 90 Axis 180 

— 1. — 1. 

— 1. 

+ 3- + 3- 

+ i.D. +2. D. 



QUESTIONS, ANSWERS AND REMARKS 183 

Calling the error plus and considering the 3. D. lens as 
artificial myopia the reduction could be figured another way and 
obtain the same results: 

Axis 90 Axis 180 

+ 1. + I. 
+ I- 

— 3- — 3. 



— i.D. — 2.D. 

for if it takes a — 1. D. C. axis 90 to correct the error in the 
horizontal meridian then the convergence is for 40 inches, 
similar reasoning applying to the vertical where the focus is 20 
inches. 



Question No. 16. By static skiametry with a + 1. D. S. 
lens before the patient's eye, if reversal occurs in the vertical 
meridian at 22 inches, and in the horizontal at 32 inches, what 
is the error? 

Answer No. 16. — 0.25 D. S. C — o«5o D. C. axis 180. 

Remarks, No. 16. An analysis of this case shows artificial 
myopia to equal 1. D. If reversal occurs in the vertical merid- 
ian at 22 inches then the refraction must be 1.75 D. of total 
myopia. Deducting 1. D. of artificial myopia leaves a true 
myopia of 0.75 D. in this meridian. 

In the horizontal meridian if reversal occurs at 32 inches 
the total refraction for this meridian is 1.25 D. Deducting 
the artificial as before leaves a true myopia of 0.25 D. C. 90, 
and by transposition the error is found to be neutralized by 
— 0.25 D. S. C — 0.50 D. C. 180. 



Question No. 17. If 52. D. S. represents the total re- 
fraction of a standard eye, where will the points of reversal be 



184 QUESTIONS, ANSWERS AND REMARKS 

by static skiametry in an eye whose measurement in the hori- 
zontal meridian is 51. D. and 53. D. in the vertical, a + 2. D. S. 
lens being used? 

Answer No. 17. Horizontal at 40 inches, vertical at 13 
inches. 

Remarks, No. 17. Of course it is known that there is no 
such thing as a standard eye, any more than there is a standard 
ear or a standard tooth, etc., but for the purpose of trying to 
think in refractive parlance 52. D. has been suggested as repre- 
senting the average emmetropic eye. This being the case, a 
meridian that shows only 51. D. is deficient 1. D. and is called 
hyperopia The meridian showing 53. D. is over the required 
refraction and is therefore plus 1. D. or "myopic." Taking 
these into consideration the problem is expressed thus: 



Axis 90 


— 1. 


+ 2. 



Axis 


180 


+ 


1. 


+ 


2. 



+ 1. +3- 



Question No. 18. In a patient having 3. D. amplitude of 
accommodation, how close to the eye (in inches) can a measure- 
ment be reliably made by dynamic skiametry? 

Answer No. 18. Not nearer than 13 inches. 

Remarks, No. 18. Donders is authority for the statement 
that the near point of distinct vision in a child 10 years of age 
is two and three-quarter inches from the eyes. This distance 
reduced to diopters gives what is called amplitude of accommo- 
dation equal to 14. D. This amplitude diminishes as age ad- 
vances, until at about 47 years of age the amplitude is only 
3. D., hence it is wise for an examiner to keep these facts well 
in mind when using dynamic skiametry, then the error will not 



QUESTIONS, ANSWERS AND REMARKS 1 85 

become confused with presbyopia when the "p p" has been 
reduced to 13 inches. 



Question No. 19. In a patient ten years of age showing 
convergent strabismus, how close to the eye should dynamic 
measurements be made? 

Answer No. 19. Ten inches is generally near enough, 
because it is inside of the usual reading point of the patient. 

Remarks, No 19. When strabismus is present, however, it 
indicates a marked disturbance between accommodation and 
convergence, and the examiner has every reason to suspect a 
pronounced error of refraction which, by the way, is not 
always found, but the examiner should proceed in a manner 
that will uncover all errors present, and if the patient is very 
young, say five years old, then a dynamic measurement up to 
within 6 or 7 inches will be wise. 



Question No. 20. By dynamic skiametry, when patients 
are from twenty to thirty-five years of age, how near should 
measurements for refractive errors usually be made ? 

Answer No. 20. About 15 inches away is near enough. 

Remarks, No. 20. In noting these different points for 
varying ages the student should exercise judgment. If the 
error is hyperopic then the nearer to the limit of amplitude an 
examination is made the more of the so-called latent will be 
uncovered. 

If the error is myopic then nearness of examination is not 
always productive of the best results, especially in cases that 
have never worn correcting lenses. 



Question No. 21. By dynamic skiametry where patients 
are from thirty-five to fifty years ^of age, how near should 
measurements for refractive errors usually be made ? 



l86 QUESTIONS, ANSWERS AND REMARKS 

Answer No. 21. Measure at two points, 13 and 40 inches. 

Remarks, No. 21. The nearer to the so-called presbyopic 
age a patient approaches the more careful an examiner should 
be to not get inside of the punctum proximum, hence data from 
two points should be made. 

Persons whose eyes are emmetropic usually do not require 
reading glasses until about their forty-seventh year of age. 
But so few eyes are really emmetropic that this age is the 
exception rather than the rule. Presbyopia, however, frequently 
serves to uncover slight hyperopic errors about the fortieth 
year of age, and this slight hyperopia is sometimes mistaken for 
presbyopia, the same as presbyopia can be mistaken for hy- 
peropia if the "p p" is lost sight of. 



Question No. 22. When patients are over fifty years of 
age, how should their eyes be measured? 

Answer No. 22. By both static and dynamic skiametry. 

Remarks, No. 22. It is quite surprising what an active 
accommodation some old persons retain, so whenever there is a 
history of eye-strain an examiner should always search deeply 
for latent errors. 

The practice of making three skiametric measurements with 
fixation at 13, 40 and 240 inches, is an excellent means for 
arriving at the correct judgment necessary to succeed. 



Question No. 23. By dynamic skiametry, how near should 
measurements for presbyopia be made ? 

Answer No. 23. Thirteen to sixteen inches, or at the usual 
reading point. 

Remarks, No. 23. Reading and working distances vary so 
with different persons that no fixed rule can be laid down for 
an examiner's guidance. Questioning a patient as to his occu- 



QUESTIONS, ANSWERS AND REMARKS 1 87 

pation and visual requirements often uncovers valuable data. 
Then following the subjective test with a skiametric examina- 
tion, where fixation and observation are at the patient's indi- 
vidual reading point, will enable the skillful examiner to quickly 
detect over and under-connections. 

It will be noted, in passing, that dynamic skiametry thus 
offers the only objective means known for measuring 
presbyopia. 



Question No. 24. By dynamic skiametry with fixation 
at 40 inches and observation at 36 inches, if emmetropia is 
present what will be the action of the shadow? 

Answer No. 24. It will move with the mirror. 

Remarks, No. 24. The quick speed of the shadow, and the 
vagueness of its definition, often show to the skillful examiner 
that he is close to the point of reversal. The difference in 
focal strength between 36 and 40 inches is only about 0.12 D., 
and it requires considerable skill to detect a difference of so 
small a quantity. 

It will be remembered, however, that in pronounced errors 
the shadows are heavy and well defined, though sluggish in 
motion, whereas, in slight errors the shadows are faint, poorly 
defined and rapid in motion. 



Question No. 25. By dynamic skiametry with -fixation 
and observation at 38 inches, if the shadow shows no movement, 
either with or against the plane mirror, what should an examiner 
do in order to determine the presence or absence of hypcrme- 
tropia? 

Answer No. 25. Add plus spheric lenses until reversal 
occurs. The strength of the added lenses just before this takes 
place will represent the error. 



1 88 QUESTIONS, ANSWERS AND REMARKS 

Remarks, No. 25. This question involves one of the 
baffling points in dynamic skiametry to many who do not go 
into the subject deeply. 

An eye with 2. D. of hyperopia in fixing at a point 40 inches 
away makes 3. D. of accommodative effort, and by skiametry 
may show no motion whatever. But if plus lenses are added 
the accommodation will relax to the point where accommodative 
myopia is a factor, when the shadow will then show an against 
motion. 



Question No. 26. By dynamic skiametry with fixation at 
40 inches and reversal in all meridians at 26 inches, what is the 
kind and amount of the error? 

Answer No. 26. 0.50 D. of myopia. 

Remarks, No. 26. This question involves two kinds of 
myopia, accommodative and true, and the difference between 
where the point of reversal ought to be and where it really is 
represents the error. 

This eye having 0.50 D. of true myopia has a punctum re- 
motum of 80 inches, and in looking at an object 40 inches away 
it would seem as though only 0.50 D. of accommodative effort 
would be used. But in fixing at 40 inches 3 degrees of con- 
vergence are called for and this, in turn, requires 1. D. of 
accommodation, so it can be readily seen why the point of 
reversal was less than that of fixation. 



Question No. 27. By dynamic skiametry with fixation and 
observation at 26 inches, if an eye accepts a plus 1.25 D. S. 
lens before reversal occurs, what is the error ? 

Answer No. 27. 1.25 D. of hypermetropia. 

Remarks, No. 27. The theories involved in this question 
cover, perhaps, the simplest principles called for in the dynamic 



QUESTIONS, ANSWERS AND REMARKS 189 

method. Fixation and observation being at a common point, 
all an examiner has to do is to find out how much accommo- 
dative relaxation he can obtain. 

An emmetropic eye in looking at an object 26 inches away 
makes an accommodative effort equal to 1.50 D. In this case, 
however, the error and the fixation called for 2.75 D. of 
accommodation, and so when a lens of plus 1.25 D. S. was 
given the accommodation then relaxed this amount. And the 
reason it did not relax more than this was because convergence 
locked it, by interfering with a further surrender until con- 
vergence was altered. 



Question No. 28. Now, suppose the case in Question No. 
2J had. shown a hyperopic error of 0.75 D. by the static 
method, how would this difference be explained ? 

Answer No. 28. As a spasm of accommodation. The dif- 
ference being what is called a latent error. 

Remarks, No. 28. Here is a question in which tension of 
accommodation is a factor. While the eyes are fixing at a 
distance it is found that 0.75 D. is all the relaxation that can 
be obtained, but when this same eye is exerted for a focal 
adjustment of 26 inches then the relaxation is more, and if the 
fixation was still nearer perhaps the relaxation would be slightly 
greater. 

It is this known data for different distances that enables an 
examiner to formulate a better prescription than if the data was 
limited to, say, subjective tests alone. 

In dynamic skiametry it is not contended that the relation- 
ship between accommodation and convergence is a fixed quan- 
tity. The "1 to 3" standard is merely used to aid in explana- 
tion. Esophoria and exophoria are factors, of course, the same 
as myopia and hyperopia. And it is the determination of the 



ICKD QUESTIONS, ANSWERS AND REMARKS 

special relationship in individual cases that makes dynamic 
skiametry of such great value for, after all, every case can be 
truthfully called "special." 



Question No. 29. By dynamic skiametry with fixation 
and observation at 40 inches, suppose a plus 1. D. S. lens can 
be added before reversal occurs, but at 16 inches a plus 1.50 
D. S. lens can be used before reversal takes place, what condi- 
tion does this indicate? 

Answer No. 29. Either so-called latent hyperopia, or an 
abnormal relationship between accommodation and convergence, 
sometimes termed "sub-normal presbyopia!' 

Remarks, No. 29. The old saying that "A rose by any 
other name smells just as sweet," is applicable in the above 
case, for it really matters little, in a practical sense, whether 
the need of stronger glasses in reading, than are required for 
distance, is due to early presbyopia, esophoria or latent hyper- 
opia. What an examiner really desires to find out are the facts 
in the case, so he can govern his judgment accordingly. 



Question No. 30. By dynamic skiametry with fixation and 
observation at 37 inches, if it takes a plus 1. D. lens to cause 
reversal in the vertical meridian, and a plus 1.50 D. lens to 
cause reversal in the horizontal, what is the error? 

Answer No. 30. 1. D. of hyperopia and 0.50 D. of hyper- 
opic astigmia, at axis 90. 

Remarks, No. 30. This is a case of measuring the two 
chief meridians of the eye. The least refractive error repre- 
sents the spheric quantity, while the difference between the 
two represents the cylindric, the axis, of course, being in the 
direction of least error. 



QUESTIONS, ANSWERS AND REMARKS I9I 

Question No. 31. By dynamic skiametry with fixation at 
40 inches, the patient wearing a plus 1. D. S. lens, if reversal 
is found at 22 inches, what is the kind and amount of the error ? 

Answer No. 31. 0.25 D. of hyperopia. 

Remarks, No. 31. This question involves two kinds of 
myopia, accommodative and artificial. The accommodative 
represents 1. D. and the artificial, 1. D., while the total is 
shown by the reversal point to be only 1.75 D., hence it fol- 
lows that hyperopia must be present to absorb the difference 
between the sum of the accommodative and the artificial myopia, 
which equals 2. D., and that represented by the reversal point, 
of 1.75 D. 

If the reversal point had been at 18 inches then the error 
would have been 0.25 D. of true myopia. 



Question No. 32. By dynamic skiametry with fixation at 
40 inches and reversal in the vertical meridian at 22 inches, and 
in the horizontal at 32 inches, what is the formula of the lens 
that will neutralize this error? The formula may be written 
two ways. 

Answer No. 32. 

— 0.25 D. S. C — 0.50 D. C. 180, or 
„ — 0.75 D. S. C + 0.50 D. C. 90. 

Remarks, No. 32. With fixation equal to 1. D. and re- 
versal at 1.75 D. the error in the vertical meridian can be cor- 
rected with — 0.75 D. C. axis 180. And with fixation equal to 
I. D. and reversal at 1.25 D. in the horizontal the error is 
correctable with a lens of — 0.25 D. C. axis 90. These crossed 
cylinders transposed equal the formulas given in the answer. 

Ray-value corrections, or where the distance that reversal 
occurs is noted, can always be proven by lens-value ones, or 
where lenses are used to produce reversal, by simply using the 



192 QUESTIONS, ANSWERS AND REMARKS 

lenses called for by the formula and then noting whether the 
shadow behaves the same as it would in emmetropia. 



Question No. 33. By dynamic skiametry, with fixation 
and observation the same, where patient is wearing a lens 
measuring + 0.25 D. S. 3 + °-5° D. C. axis 150 and it is found 
that an added lens power equal to + 0- 2 5 D- S. can be given 
in the 60th meridian before reversal occurs, but this same lens 
causes motion against in the 150th merdian, what is the correct 
formula ? 

Answer No. 33. + 0.25 D. S. C + 0.75 D. C. 150. 

Remarks, No. 33. The patient's lens, as above, reduced to 
its cylindric equivalent gives a total of 

Axis 60 Axis 150 

+ 0.25 + 0.75 

If an added + 0.25 D. can be given in the 60th meridian, but 
not in the 150th, then 0.25 D. C. axis 150 is to be added to the 
patient's lens for a new formula and this transposed gives 
the answer. 

Measurements made over a patient's own glasses offer a 
very convenient means for quickly determining whether they 
are correct or not. 

Question No. 34. By dynamic skiametry where patient is 
wearing a lens of — 0.50 D. S. C — 0.87 D. C. axis 105 
and it is found that a combination of + 0.12 D. S. 3 — 0.25 
D. C. axis 15 is required to give a slight motion with in all 
meridians, fixation and observation being the same, and made 
at 16 and 40-inch distances, what are the correct formulas that 
may be given? 

Answer No. 34. 

— 0.63 D. C. C — 1-25 D. C. 105. 

— 0.63 D. S. C — 0.63 D. C. 105. 

— 1.25 D. S. C + 0.63 D. C. 15. 



QUESTIONS, ANSWERS AND REMARKS 193 

Remarks, No. 34. The cylindric equivalent of the patient's 
lens together with the added quantity shows : 

Axis 15 Axis 105 

— 0.50 — 0.50 
+ 0.12 — 0.87 

— 0.25 + 0.12 



— 0.63 — 1.25 

Transposition then follows. 



Question No. 35. By dynamic skiametry, why should all 
measurements be made in a binocular manner, that is, by meas- 
uring first one eye then the other, then back to the first one 
again, and then to the second, and so on, with and without 
covering either eye ? 

Answer No. 35. To insure uniform muscular relaxation. 

Remarks, No. 35. This question involves co-ordinate fixa- 
tion, for as one hand is usually more active than the other so 
is one eye usually more active than its mate, the most active 
one being called the "fixing eye" the other lagging along until 
compelled to exert itself. 

It is said that in cases of convergent strabismus, due to hy- 
peropia, if the fixing eye has its refractive error fully neutral- 
ized with lenses the straightening will occur even where no 
correction is given for the deviating eye. Thus showing the 
supremacy of the eye of fixation. 

At the beginning of a skiametric examination the operator 
can not tell which eye has the best vision, as this is left for the 
subjective test to determine, and so it sometimes happens that 
the eye with the greatest error is the one of fixation. It will 
be seen, then, how important it is for the skiametrist to make 
his examination in the manner here referred to. 



194 QUESTIONS, ANSWERS AND REMARKS 

Question No. 36. With an esophoria of 6 degrees, what 
kind and amount of refractive error should a patient have in 
order to theoretically harmonize his accommodation. 

Answer No. 36. About 2. D. of myopia. 

Remarks, No. 36. From the foregoing it will be seen how 
unwise it is to adapt prisms when the myopia present has never 
been corrected. 

A wise procedure in all heterophoric cases, undergoing their 
first examination, is to give correction for the refractive errors 
found, and then to await nature's effort to adapt herself to the 
new order of relationship between accommodation and con- 
vergence. 

Prisms may have to be given in the end, but they should 
never be adapted at a first sitting if it can possibly be avoided. 



Question No. 37. With 2. D. of hyperopia what kind and 
amount of heterophoria should be present in order to theoret- 
ically harmonize the patient's convergence ? 

Answer No. 37. About 6 degrees of exophoria. 

Remarks, No. 37. This is the opposite of Question No. 36. 
If 2. D. of accommodation calls for 6 degrees of convergence, 
then an eye that makes 2. D. of accommodation for infinity 
must suppress this 6 degrees, or else be exophoric this amount, 
hence it follows that suppressed convergence shows theoretic 
divergence. 

Extrinsic muscles that are mal-attached, or are affected by 
paralysis, do not, of course, come under the same treatment 
as those involving errors of refraction and the consequent dis- 
turbance in their correlation with the intrinsic muscles. 

It is plain, to be sure, that an examiner at a first sitting does 
not know the true cause of whatever heterophoria he may find, 



QUESTIONS, ANSWERS AND REMARKS 1% 

but if a marked uncorrected error of refraction is present it 
behooves him to neutralize as much of this error as he can 
before resorting to prisms. 



Question No. 38. Why is convergent strabismus some- 
times a concomitant of high degrees of hyperopia? 

Answer No. 38^ Because in the excessive muscular effort- 
put forward by the accommodation, in order to neutralize the 
error, the convergence is overexerted, too, and then the patient 
unconsciously learns to see better with the fixing eye by sup- 
pressing vision in the deviating one, thus permitting it to turnj 
inward as far as it likes. 

Remarks, No. 38. In convergent strabismus cases, while 
vision is often suppressed, the extrinsic muscle action is not, 
and this therefore accounts for the marked deviation from the 
standards controlling normal co-ordination. 



Question No. 39. Why is divergent strabismus sometimes 
a concomitant of high degrees of myopia? 

Answer No. 39. Because, owing to the non-use of accom- 
modation, intrinsic muscular effort is not required to produce 
focal adjustment. Convergence thus failing to receive asso- 
ciate stimulation lags behind and, frequently, one eye learns 
to suppress vision, thereby losing its power of co-ordination. 

Remarks, No. 39. Short explanations of what might be 
called long subjects may be pleasing to students, but they are 
often misleading on account of their very shortness. For this 
reason all searches after optometric facts are counseled to delve 
deeply into the underlying causes responsible for disturbed re- 
lationships between accommodation and convergence, in all sorts 
and conditions of cases. 



^^m^bhbh^MB^^HHHBB 



I96 QUESTIONS, ANSWERS AND REMARKS 

The subjects of heterophoria and heterotopia have been 
touched upon here simply because of their being aggravated 
phases of many lesser disturbances due to the common source 
of inco-ordinate accommodation and convergence. 



Question No. 40. What is the relative value of objective 
optometric methods as compared to subjective ones? 

Answer No. 40. As one is to one. 

Remarks, No. 40. Every optometric method of merit be- 
comes useful to the optometrist in some case at some time. 
It therefore behooves all ambitious examiners to thoroughly 
acquaint themselves with the principles underlying every opto- 
metric method, as this places them in a position to be able to 
judge for themselves, for, while the taking of ocular measure- 
ments is often comparatively easy, it is the formation of cor- 
rect judgment that in the end can be said to make an examiner's 
ireputation, while if incorrect it may break it. 



CHAPTER XII. 

Opinions of Others Regarding the Value of Skiametry 
in General and the Dynamic Method in Particular, 
With Comments on Objective Versus Subjective 
Optometry, and the Relationship of Accommodation 
and Convergence. — Including Quotations on Men- 
tal Perception, and an Epilogue. 

No matter how meritorious a method may be there are 
always some well-meaning persons who prefer to hear the 
opinions of others first, and if these expressions are favorable 
they feel warranted in taking up the subject themselves with a 
view to its mastery. Then, too, there are the "Doubting 
Thomases" who sometimes get started on the wrong line of 
reasoning and become sadly tangled, due, perhaps, to some early 
misconceptions. It may be truthfully stated, however, that all 
reasoners unquestionably try hard to do a subject justice, and 
for this reason their arguments, like the logic of an opposing 
attorney, is well worth listening to, therefore, before closing 
this little volume, it is thought best to hear all sides regarding 
dynamic skiametry by quoting from sources independent of the 
author, and in this way the pros and cons may serve a useful 
purpose. The following selections have therefore been made: 

OPINIONS OF OTHERS. A. W. Stammer, in the London 
Optician, for April, 1910, writes: 

"I want to describe one or two simple experiments that any 
optician with a test case can try, and which will give him a better 
idea of the way in which the extrinsic muscles work than will weeks 



■nai^iHai^i^Bi 



I98 OPINIONS OF OTHERS 

of book study. In all that follows it must be remembered- that the 
optical instrument theory is completely ignored, and later it will be 
seen why. 

"The first text book statement that does nothing but confuse stu- 
dents is that there is a definite co-relation between the functions of 
accommodation and convergence. This is absolutely true as far as it goes, 
and while you regard the eye as an instrument conforming to mathe- 
matical laws requires no modification. It was once believed that 
there was a co-relation so perfect that someone brought out a system 
of testing called dynamic skiascopy that was based on this fact. 
That system failed for the reason that there is no fixed relation 
between these two functions. Try the following experiments your- 
self, and I think you will see what I mean. 

"Look at the distance test charts through a pair of minus two 
spheres and you will see each letter quite single. You are accommo- 
dating to the amount of two dioptrics, but you are not converging, 
or you would see everything double. If it were not possible to use 
these two functions independently, no living person who was hyper- 
metropic could see anything single. Again ; look at the chart through 
a pair of six degree prisms base out, and you will still see things 
single and quite clear. If you were accommodating you would be 
for the time being myopic and it would be necessary for you to use minus 
lenses to see the chart clearly. You will see for yourself that it is not 
so; I can myself read 6/6 with a ten degree prism base out in each 
eye. This is found in daily practice in the case of a presbyope who 
reads at thirteen inches with a + 3.0 addition for reading. In all 
presbyopes of a certain age there is convergence for the reading dis- 
tance with absolutely no accommodation. 

"Now, your first experiment proved that you can accommodate 
and not converge, and the second that you can converge and not 
accommodate. What does control the co-relation of these two func- 
tions? Simply this, the desire first for single vision, and then for 
clear vision ; and these results are obtained by co-relation between the 
brain and the retina." 

The Optical Journal for May 26, 1910, contained the fol- 
lowing from F. A. Wambold: 

"It is certainly true that testing by dynamic skiascopy is a failure. 
It always will be; but the reason is not found in the fact that there 
is no fixed relation between convergence and accommodation ; no 



OPINIONS OF OTHERS 199 

such fact exists. The opposite is true, as nature made those two 
functions work automatically. 

"It seems so reasonable, so natural, to think they work in partner- 
ship. They are controlled by the same wires, the third nerve through 
which the nervous energy is applied. It is the nervous supply way 
back in the brain that gives power to those intrinsic and extrinsic 
muscles, and to the recti interni and externi. The same supply that 
runs the whole machinery also gives power to the muscles that operate 
the crystalline lens and the eyeball, to cause the lens to bulge out, 
and to turn the eye out again when turned in. 

"In solving that question of association of convergence and accom- 
modation, we must not forget the function of the recti externi muscles 
which get their supply by way of the sixth nerve. 

"Try the same experiments suggested by Mr. A. W. Stammer. 
Put those same minus 2 spheres in front of your eyes and look at the 
test chart. If you have the power to overcome the glass, and in 
addition any defect you may happen to have, you will of course not 
see double. Vision will be single. Why? Not because there has been 
no convergence in response to the accommodation that was necessary 
to bring the foci on the retina. No, not that ; they had converged ; 
they should have and they did. The wattage that went over the 
wires of the third nerve to the ciliary went also over the same wires 
to the recti interni muscles, and pulled the eyes in at the same ratio 
the force was applied to the ciliary. 

"But that created a condition that should not be, and in goes the 
message to the brain center to turn on the power on the sixth line 
that controls the externi, and the eyes are pulled straight again. 
That's why you do not see double, why you have single vision looking 
through that minus 2 lens. If this were not the case, that is, if those 
muscles had not that function, that duty, then it would have been 
conclusive and logical to say, 'no living person who was hypermetropic 
could see anything single.' 

"For the same reason you see things single looking through a six 
degree prism. The prism, base out, turns the eyes in and forces the 
accommodation, and vision would be blurred if it weren't for the fact 
that nervous energy applied by way of the sixth nerve through the 
externi pulled them straight again. It will do it every time, provided 
the supply is equal to the demand. 

"So you see plainly that said conclusions are based on false 
grounds and test must fall. 



■■^^■^■HH 



200 OPINIONS OF OTHERS 

"Look at this statement : 'If they converge, they will see double 
and the retina will at once inform the brain of the fact, and the recti 
interni will receive instructions to relax until the image on each eye 
is on the fovea.' 

"I will concede the first, but deny the return message, 'the instruc- 
tion given by the brain to relax.' The brain knows better. It knows 
what those externi muscles are there for, and turns on the nerve 
wattages on the sixth nerve to stimulate those outer muscles to turn 
the eyes straight — and straight they come. That is the function of those 
muscles. We must then not forget and disregard the function of the 
recti externi. Of course, that means an extra supply to be turned 
on in that direction. If the supply be insufficient the eyes will remain 
converging and the person will see double. Contraction is not the 
cause that turns the eyes in, it is an exhibit of the nervous energy 
applied. The nervous energy going over the same wires that control 
the accommodating and converging muscles are the causative factors. 
The nerve-wattage turned on the sixth nerve neutralizes the first 
exhibit and eyes come straight. See ! It is true that said interni 
muscles relax, but not in response to any direct instruction from the 
brain to do so. It does it because of the negative pull against it 
which exactly neutralizes its contracting effort; the muscles are not 
to blame. 

"The automatic relationship of convergence and accommodation 
stands. Why dynamic skiascopy is a failure; that is another story. 
The failure to understand this phenomenon has another reason. It 
is a lack of a correct and complete understanding of the physical 
laws of optics." 

Mr. H. B. Moore, in a paper read before the Colorado State 
Optical Society, July, 1910, stated as follows : 

"The static method is to place a + I0 ° D. lens in the trial frame 
in front of each eye; then rotate the mirror at a distance of 40 inches 
from the eye, requesting the patient to look at the test card 20 feet 
away, and if the shadow remains still in the meridians, then the case 
is emmetropic, as the -j- 1.00 D. lens just neutralizes the distance 
between the optometrist and the patient. If the shadow moves with 
the mirror, the case is hyperopic, and if it moves against, it is myopic, 
and from all retinoscopic findings in this method, a -f- 1.00 D. should 
be deducted. 



OPINIONS OF OTHERS 201 

"The dynamic method is just the reverse of the static, and a 
system of shadow testing where the accommodation is active. In 
this method the patient is directed to read a small card of different 
size letters, placed on the forehead of the optometrist 40 inches away; 
now to do this he has to use 1.00 D. of his accommodation. Now, 
let the deep-thinking optometrist follow this explanation closely, then 
he can judge as to the real value of this method, as it is the writer's 
intention to give facts and prove that this method, which seems so 
nice in theory, does not meet with accurate results when in prac- 
tical use. 

"Here are a few examples as follows — first case : if the eye is emme- 
tropic the rays of light will emerge parallel and the 1.00 D. of accom- 
modation will converge these rays and cause them to focus at a dis- 
tance of 40 inches and no motion will be observed in either meridian, 
as the 1.00 D. of accommodation used takes the place of the -f- 1.00 D. 
lens that is used in the static method. 

"Second case: if the patient has 1.00 D. of hyperopia he will be 
obliged to use 1.00 D. of his accommodation to see the test card 
clearly at a distance of 20 feet and 1.00 D. to read the brow card at a 
distance of 40 inches, thus making a total of 2.00 D. of accommo- 
dation used. 

"Third case: suppose a patient has 1.00 D. of myopia ; his far 
point for distance vision is 40 inches and the emergent rays will focus 
at this point, and the patient will not use any accommodation to read 
the brow card. 

"Now, it is claimed by the exponents of the dynamic method that 
it is impossible to separate accommodation and convergence by placing 
the plus lenses in front of the eyes, except for hyperopia they may 
have. In the first case we find the eye emmetropic using 1.00 D. of 
accommodation. They place plus lenses in front of the eye and find 
the strongest that will be accepted without reversing the shadow. In 
an emmetropic eye, they state that a -f- 0.25 D. will cause a reversal 
even though the eye is accommodating 1.00 D. 

"In the second case we find the eye using 2.00 D. of accommoda- 
tion. They claim that this eye will relax 1.00 D., for it is that much 
hyperopic, but it cannot relax any of the other 1.00 D. as the con- 
vergence checks it so it will not relax. 

"In the third case, the eye being myopic 1.00 D., no accommodation 
is in use. They place an over-correction of minus spheres, rendering 



w^mmmmm 



202 OPINIONS OF OTHERS 

the refraction of this case hyperopic. Then they gradually reduce 
with minus spheres until they find a point of reversal. 

"The special advantage claimed by the exponents of this system 
is : in case of a spasm of accommodation sometimes found in a case 
of hyperopia. The eyes will test myopic at 40 inches because the 
spasm holds the focus in front of the retina. The spasm covers the 
1.00 D. of hyperopia and renders the eye myopic 1.00 D. and at 40 
inches the motion is seen to move against the mirror. Now, advance 
the mirror to 10 inches, requesting the patient to read the brow card; 
this calls for 4.00 D. of accommodation, and as the patient has a 
spasm of 2.00 D. covering his 1.00 D. of hyperopia, thus bringing the 
focus 1. 00 D. in front of the retina, so it will only be necessary for 
him to use 3.00 D. of his accommodation. This absorbs the spasm and 
gives a chance to measure as much as 3.00 D. of hyperopia ; but right 
here. the dynamic exponents claim that he will accept just 1.00 D., as 
this is the amount of his hyperopia and that his convergence checks 
the relaxation at this point; but does it? 

"This whole system hinges upon their theory that accommodation 
and convergence are so closely related that by placing plus lenses in 
front of the eyes this relation cannot be disturbed. If we allow the 
exponents their premise in an argument, we generally have to admit it, 
as their reasoning will be logical all the way through. If right here 
we take pains to experiment so we can determine the truthfulness of 
their first proposition then we will discover why this method proves 
up inaccurate in nearly 90 per cent, of all its cases. The writer 
states fearlessly that convergence is not a check upon accommodation 
and will prove it by the following experiments : 

"Now, listen: if the exponents are right in the relation of these 
two functions in their shadow test, it surely ought to be demonstrated 
with lenses subjectively. Take persons with emmetropic eyes and if 
we place — 2.50 D. spheres in front of their eyes, and in order that 
they can read the 20/20 line, on the test card 20 feet away, they will 
have to use 2.00 D. of their accommodation. The 20/20 line on the 
test card 20 feet away is perfectly plain, bearing in mind that their 
accommodation is fixed for 16 inches. This ought to prove most 
conclusively to any optometrist that under the above-named condi- 
tions the accommodation can be exercised 2.50 D. while the con- 
vergence remains fixed for 20 feet. If we were to increase the strength 



OPINIONS OF OTHERS 203 

of the minus spheres, it would produce diplopia, thus showing that 
2.50 D. is the limit of their power of separation between these two 
functions. 

"In another experiment we find that they can read the 20/20 line 
perfectly with 25 degree prisms (half of the amount over each eye) 
base out. This shows that they can send a nerve force to the internal 
muscles without affecting the ciliary muscles in the least. It seems to 
the writer as if these two last experiments, which can be made on 
yourself or anyone else, ought to convince any deep-thinking optom- 
etrist of the inaccuracy of the theory of the dynamic method. 

"In all cases of hyperopia, except the 'squints,' we find these two 
functions working entirely out of harmony with each other, showing 
the wonderful power of adjustment in nature. In all cases of myopia 
we have the same conditions reversed, for while the convergence is 
fixed for 20 feet, the accommodation is nearer to the eye according 
to the myopia." 

In giving his opinion as to what constituted the best ski- 
ametric method, Mr. Moore further stated : 

"The fogging method of retinoscopy is one that relaxes all accom- 
modation, as it is an active accommodation that is responsible for 
many errors in refraction. The test is made by placing a plus 4.00 D. 
lens before the eyes and having the patient look off into space. This 
renders the eyes myopic and puts them in a condition of rest. If 
the eyes are emmetropic, the emergent rays will be parallel and a + 
4.00 D. sphere will bring these parallel rays to a focus at 10 inches in 
front of the lens. As you observe the motion of the shadow from 40 
inches, you will find the eye decidedly myopic. Move closer and closer 
until you reach the point of no motion. Measure from the lens to the 
mirror, and if the eyes are emmetropic you will find the neutral point 
or conjugate foci to be 10 inches. If your case happens to be hyper- 
opic of 1. 00 D. the rays of light will emerge 1.00 D. divergent; as it 
requires 1.00 D. of your -f- 4.00 D. to make these rays parallel, they 
will be brought to a focus 13 inches from the eye. The motion will 
reverse at this point. In all cases of myopia the emergent rays are 
convergent and the + 4.00 D. will make them still more convergent. 
If there is 1.00 D. of myopia, the convergent rays would focus at 40 
inches without any lens. Placing a 4.00 D. sphere in front of the eye 
causes the rays to focus at 8 inches in front of the lens. 



204 OPINIONS OF OTHERS 

"If we wish to be exact in our measurements in this or other 
methods we can attach a tape measure to our trial frame and hold 
the same in one hand, while we rotate the mirror with the other, at 
the required distance. In the fogging method this will give you the 
exact distance between the lens and the mirror and you will find your 
conjugate foci. The rule to follows is: place a + 4.00 D. sphere in 
front of both eyes. Reflect the light with a plane mirror into the eye 
and find the point where there is no motion. If it is at the focal 
point of the lens 10 inches, the eye is emmetropic." 

Mr. R. M. Lockwood, of New York, the scientific editor 
of the Optical Journal, in a lecture on ''Dynamic Optometry," 
before the Optometric Society of the City of New York, March 
9, 1910, among other things, said: 

"The first variety of dynamic optometry, to which attention has. 
been called in recent years, is the dynamic test with the skiascope, 
called by the deviser of the system, A. Jay Cross, of New York, 
'dynamic skiametry,' and elucidated and discussed in his work, 'A 
System of Ocular Skiametry/ 

"The practice of dynamic skiametry is based on the theoretically 
strong inter-relation of accommodation and convergence, so that if a 
fixation chart be placed at some point which is near to the eyes under 
test the accommodation for that distance and the convergence neces- 
sary for the same distance will act together with the result that, when 
the neutralizing lens has been found for that distance, the lenses in 
the frame will be the correction for distance, without any allow- 
ance being made for the point at which the test is made. As will be 
seen, the fundamental difference between the static method and 
dynamic skiametry is that with the static test the fixation chart, if any 
is used, is twenty feet away, while with the dynamic method the 
fixation chart is brought to approximately the plane of the observer's, 
eye. In this latter case it is claimed that there is a certain amount 
of the accommodation exerted which will not relax, and this is due to 
the fact that the accommodation and the convergence are acting to- 
gether, and that the relation between these two functions is a very 
strong one. 

"Suppose we find, with the fixation chart attached to the skiascope, 
that it requires a plus 1.50 sphere to make the shadow neutral; then,, 
according to the theory of dynamic skiametry, plus 1.50 is the cor- 
rection for distance, unless the accommodation is deficient, no matter 



OPINIONS OF OTHERS 205 

at what point the test is made. Suppose the test is made at twenty 
inches from the patient's eye, then, the fact that he is accommodating 
for twenty inches and converging for twenty inches means that the 
ciliary exerts two diopters of accommodation which it will not relax 
so long as the fixation chart over the skiascope is fixed, but as this two 
diopters will relax when the attention passes from this chart to the 
distance, then the correction in the frame is the correction for dis- 
tance, the accommodation supplying the amount of power necessary to 
have the attention come up from distance to the plane of the chart. 
The author of_ dynamic skiametry claims that part of this accommo- 
dation, exerted because of the near location of the chart and the inter- 
action of accommodation and convergence, will be the ciliary spasm 
present, if any ; so that in this supposed case the two diopters of accom- 
modation exerted because of the location of the fixation chart will be 
made up of the amount of the spasm and in addition the necessary 
extra effort required to make up the full amount; hence the method, he 
claims, is an infallible detector of ciliary spasm, and if the full cor- 
rection as shown in the trial frame cannot be worn at first it may in 
time, when the spasm wears off, if it ever does. Incidentally it is found 
according to this theory that spasm of the accommodation is a wide- 
spread condition in eyes. 

"Now, I have explained the fundamental point of dynamic ski- 
ametry as the author gives it, though I do not accept it that way. I 
appreciate the great value of the method, and it was the consideration 
of this method over a space of many months that led me to the for- 
mulating of another theory, which not only takes in dynamic tests 
with the skiascope, but similar tests with the trial-case lenses, both of 
which I have grouped under the term 'dynamic optometry,' meaning 
the act of testing eyes with the accommodation purposely in force for 
the purpose of finding that correction which will be harmonious for 
any selected distance without either the innervations involved being 
too great or too little; or, in other words, the finding that correction 
which will give comfortable vision." 

T. G. Atkinson, M.D., of Chicago, editor of the Medical 
Standard, and of the Optometric Department of the National 
Jezveler and Optician, in the issue of the latter publication for 
August, 1909, says, in part : 

"Speaking seriously, we do not believe that the importance and 
significance of dynamic skiametry is anything like properly appreciated, 



206 OPINIONS OF OTHERS 

even by those who are capable of grasping its import. It is, in our 
judgment, by far the most momentous step in optometry since the days 
of Donders. Indeed, as we have previously remarked, it constitutes 
the line of demarcation between the old and new optometry, just as 
definitely as the spectroscope divides the old and new astronomy, and 
in much the same way, for the essence of djmamic skiametry, like that 
of spectroscopy, is that it furnishes a working method of measuring 
objective phenomena in active process. It is not alone the useful and 
valuable things which it enables the optometrist to do that gives far- 
reaching importance to the Cross system, but the revolutionary stand- 
point that it establishes, from which to approach and handle problems 
yet to arise. 

"Specifically, the most notable practical advantages afforded by the 
dynamic system of skiametry are, first, that it furnishes an exact 
method of measuring refraction as it actually is, without any allow- 
ances for the ciliary muscle, and second, that it utilizes the well known 
principle of kinetic synergism, by which an active muscle will readily 
accept needed relief. A further advantage of the system, secondary 
from an optical point of view, but of prime importance from the 
optometrist's standpoint, is that it is the only method by which ob- 
jective refraction can be reliably carried out without a cycloplegic, so 
that it is really a crucial, let us say the crucial, pivot around which 
revolves the entire sphere of optometry as an independent planet. 

"Eventually, every optometrist will have to understand and practice 
dynamic skiametry. Eventually, so will every medical man who hopes 
to maintain his standing as a refractionist. The medical profession is 
foolishly engaged in the ostrich tactics of burying its head and shut- 
ting the new order of things out of vision, and will some day with- 
draw its silly head to find that it is outflanked and outdistanced. But 
there is nothing to exempt from the same fate the equally foolish 
optometrist who, while he recognizes the importance of the dynamic 
system and pays lip tribute to its author, neglects to avail himself of 
its principles and practice." 

Dr. H. J. Cook, ex-president of the American Optical Asso- 
ciation, in a paper read before the Tennessee State Optical 
Society, July, 1910, gave his opinion of dynamic skiametry in 
the following words : 

"In cracking some nuts along this line I will take some of the 
conundrums that have been given from time to time in the optical 



OPINIONS OF OTHERS 207 

publications and try to explain them by the aid of a set of rules 
which I gave before this body last year at Nashville, in more detailed 
form. It must be understood that 'rules' do not govern the shadow 
tests any more than they govern trial-case refraction, but they will be 
found a great help to the beginner in skiametry, as they fix the prin- 
ciples in the mind in the same way that the jingle of old times fixed 
the odd days of the months, 'Thirty days hath September, April, June 
and November.' This great discovery of A, Jay Cross is the only 
method by which the total refraction of an eye can be estimated 
without the use of drugs. It is the only objective method that can be 
used in presbyopia. It can uncover spasm when all other systems fail. 
Its value is so great that it seems a waste of time to say that every 
refractionist should use it — at least in corroboration of other methods. 

"I take it that you are familiar with shadow appearance, shadow 
motion, mirrors, lights, dark room accessories, and, above all, with the 
laws relating to conjugate foci. We are taught that rays from an 
object emerge from the eye along the same path by which they 
entered it; thus the parallel rays emerging from the emmetropic eye 
and the divergent rays from the hyperopic eye must be made con- 
vergent in order to be intercepted at the crossing point by the 
mirror of the observer. As shadow reversal is at the focus conjugate 
with the retina, we must set up some form of myopia where real 
myopia does not exist. We have two ways of doing this: by fixation 
(or 'accommodative myopia') or by plus lenses (artificial 'myopia'). 
We can deal with all three of the myopias, singly or combined. 

"Though the real myope uses his accommodation less than the 
emmetrope, and the emmetrope less than the hyperope — the addition 
of artificial myopia to any of these by lenses, or by accommodation, 
increases proportionately the dioptric value of the media traversed by 
the rays from our mirror, and decreases proportionately the distance 
at which shadow reversal is located; hence we are to base our 
diagnosis of refractive errors upon differences between the actual 
location of reversal and the point where normally it should be found 
in conjunction with the myopia we have added. Hence the following 
rules : 

"i. Fixation distance (accommodation) or plus lenses, or both, 
must be used to set up the incident focal point. 

"2. Lenses and accommodation are added together in their values 
to create a myopic far point (point of reversal). 



20S OPINIONS OF OTHERS 

"3. Fixation and reversal points at same distance indicate emme- 
tropia, or if brought together with plus lenses, corrected ametropia. 

"4. Reversal found beyond fixation indicates hyperopia. 

"5. Reversal found inside fixation indicates myopia. 

"6. In presbyopia neutral point falls behind fixation, as hyperopia. 

"The following 'nuts' were given in the Optical Journal, page 839, 
by A. W. Stammer in an argument to discredit the dynamic system 
on the ground that accommodation and convergence are variable and 
can be used independently. For this reason he condemns the system 
as worthless, and cites the following cases to prove his claim: 

"Case 1. Emmetrope wearing minus 2. D. reads 2o/2oths without 
convergence, but is using 2. D. accommodation alone. 

"Case 2. Same emmetrope wears 6-degree prisms before each eye 
base out; can see normally at distance type without accommodation 
■while strongly converging. 

"Inasmuch as dioptric values and not convergence govern in 
shadow behavior, his condemnation of the system is based upon error. 
In neither case has one of the 'myopias' been set up, as required 
Dy rule 1. 

"In case 1, the two diopters of accommodative effort was exactly 
balanced by the 2. D. of artificial hyperopia caused by the minus lens, 
thus nothing was added to the dioptric value. 

"Case 2 comes under the same conditions. Rule 1 proves it. Con- 
vergence added no dioptric value to the eye in these exceptional cases, 
and in case 2, it is to see that the converging lines only extended 
to the outer surface of the prisms, becoming parallel thereafter. 

"Quizzes have gone the rounds of optical publications tending to 
mystify those who do not dig deeply. 

"Case 3. One of these asks, 'How can you get reversal of shadow 
at a fixation point, say 40 inches, from an hyperope of 1. D., while 
wearing his correction which makes him an emmetrope?' 

"According to rule 1, accommodative myopia of 1. D. has been 
added to this eye by fixation, and another 1. D. by the plus lens, 
— 2. D. in all. If the case was an emmetrope this 2. D. addition 
would bring the reversal point up to 20 inches, the same as in real 
myopia without artificial aid. But his hyperopic divergency consumes 
1. D. of the added power to bring the divergent lines to parallelism, 
while the remaining 1. D. can only bring reversal up to the fixation 
point of 40 inches. This accords with rules 1, 2, 3 and 4. 



OPINIONS OF OTHERS 20O, 

"Case 4. Cases which seem to disprove rules should be carefully 
examined. One in which distant vision blurs with the weakest plus 
lens, but is improved with a weak minus lens is a hard nut for trial 
case. Suppose mirror shows reversal at 32 inches while fixation is at 
40 inches, for example. By rule 5 we suspect myopia, because reversal 
is found inside fixation. We move fixation card up to this reversal 
point, when, if true myopia exists, reversal is found at a correspond- 
ing distance forward (nearer patient), which will be in accordance 
with the dioptric value added, or 26 inches. If, instead of this forward 
movement, we find that reversal has lagged behind, we may expect 
spasm. Moving fixation card still nearer, say to the 26-inch reversal 
point, if the case is spasm, of the amount shown by the previous trial 
lens used, reversal will now be found behind the normally expected 
position, and will prove hyperopia, as per rules 1 and 4. 

"In cases like this, the spasm has been completely swallowed up in 
the effort forced by close fixation, which was used in excess of the 
false myopia caused by the spasmodic effort. These cases are not rare, 
and should teach us to not stop at reversal, but use several close 
fixation points to corroborate, remembering that the principle is the 
same as in trial-case work, where we use the strongest plus at infinity, 
with which we get normal vision. 

"I would not urge the use of this system in presbyopia, owing to 
the small pupils usually found, but this is a form of hyperopia, and 
premature presbyopia may often be found in people young enough to 
be carelessly credited with the average accommodation given in 
Donders' table, and it is not rare therefore, in using the system, to 
find cases of young people who need stronger glasses for reading than 
for distance. 

"The near point can be located, as well as the desired reading dis- 
tance in presbyopia, by dynamic skiametry." 

In a paper on "Retinoscopy," by A. R. Slader, read before 
the Vermont State Optical Society, in July, 1910, he says: 

"As I have mentioned previously, and as all optometrists know, 
there are two distinct methods of making the test, called the static 
and dynamic. The static supposes the eye of the subject at rest — 
the accommodation being inactive — the focus being at infinity. By the 
dynamic method the accommodation is in force, the fixation being 
inside of infinity at a certain definite point. By the static method the 
eye tested is made artificially myopic by means of a plus lens repre- 



210 OPINIONS OF OTHERS 

senting the distance the test is made inside of infinity; +0.50 for 80 ins. 
or 2 meters, + i-oo for 40 ins., or one meter, + i-So for 26 ins., + 2.00 
for 20 ins., etc. By the dynamic method the lens of the eye takes the 
place of the artificial lens, the eye being held to its position by means 
of a brow card or lettering on a standard that can be placed at any 
desired distance either back of the observer or in front of him. In 
using the static method myself I usually work at 40 ins. and place a 
-f- 1.00 D. lens before the eye examined at once, then no deductions or 
changes are needed to be made at the close of the test, but simply the 
removal of the lens. 

"The two methods differ only as regards the treatment of the 
accommodation of the subject. By the one it is suppressed; by the 
other it is put into action. When it is suppressed it is always a ques- 
tion whether it is fully suppressed or whether it is not exerted to a 
more or less degree. Especially is this true regarding this function in 
young people or where there may exist what is called spasm of the 
accommodation. In subjective tests we have the same problem, as 
we all know, to confront. The oculist disposes of it with the use 
of the cycloplegic, which paralyzes the function of accommodation, 
but it is a question whether this solution is wholly a happy one in 
view of the changes which need to be made in the resultant lenses to 
make them wearable, and the dangerous nature of the drugs employed. 

"In static retinoscopy the darkened room helps to control the 
accommodation. Then some use the fogging method, placing strong 
lenses before the subject's eyes at first. It rests with dynamic ski- 
ascopy, to my mind, however, to supply the best means of over- 
coming the difficulty. This method originated with A. Jay Cross, and 
is amply explained by him in his book entitled 'A System of Ocular 
Skiametry,' which should be in the hands of every optometrist. 

"By the dynamic method the accommodation of the subject is induced 
to work, and the theory is that the greater the burden placed upon these 
muscles the more inclined they are to give up any excess of energy 
which they might otherwise have exerted — that it really unlocks spasm 
of the accommodation — whether this is strictly so, or, as some assert, it 
only reveals that condition — whether between the co-ordinate functions 
of accommodation and convergence there is a fixed and immutable 
relationship — a diopter of accommodation calling for a meter angle of 
convergence, as the dynamic system theoretically implies — or, as others 
claim, it only shows whether the two functions are in harmony at a 
given point, certain it is that those who use this method regularly 



OPINIONS OF OTHERS 211 

find it of very great value and get very satisfactory results. I, myself, 
and I presume many others, use both methods, though the dynamic is 
the one most relied upon in hyperopic conditions with younger people. 

"By the dynamic the test can be made at varying distances and 
with fixation of the subject's eyes at different points. Thus, while the 
retinoscope is used at 40, ins. or 1 meter, the eyes of the subject can be 
fixed at 80 ins. or at any other point inside of infinite distance and the 
operation of the shadow noted. The size of the reflex, rapidity of the 
shadow action, etc., will vary according to where and under what con- 
ditions it is viewed, and with some eyes one position is best and with 
some another. Again, in presbyopia it can be used to determine approx- 
imately the strength of lenses needed for the near work, the examina- 
tion being made within the reading distance. 

"But all the work with the retinoscope needs to be verified with 
the subjective test. It does not dispense with that form of test, but, in 
my opinion, the two should go hand in hand. 

"In closing, I would say that I believe that every optometrist who 
attains the highest success in the profession must have a working 
knowledge of retinoscopy and use it constantly. Look at its advan- 
tages, my brother optometrists ! First of all, it is an objective method. 
Such a method appeals to the public who furnish the eyes to be 
tested. The subjective trial-case method of examination, even if 
scientific and furnishing accurate results to the skilful operator, looks 
to the customer only like a roundabout method of having him select his 
own lenses. To be able to tell a person what he needs for glasses, 
without asking him or her any questions, by the simple flashing of a 
light into the person's eyes, certainly gives the man able to do it a 
professional standing in the opinion of the client that no subjective 
test will. 

"Secondly — How simple and inexpensive the absolutely essential 
apparatus for the test is. All that is really needed is the little ordinary 
hand retinoscope — a bright light and a darkened room with the trial 
frame and lenses, that is all. Of course, adjustable chairs and other 
auxiliaries are desirable, but good results can be obtained under the 
most adverse conditions by one who is very familiar with the test and 
has become an expert. 

"Thirdly — The accuracy of tlie results — Of course much of this 
depends upon the skill of the operator — 'the man behind the gun,' 
but so it is with any instrument or system of refraction — but given the 



212 OPINIONS OF OTHERS 

skilled operator, which practice will develop, and right conditions, and 
I believe there is no method of measuring refractive errors so exact. 

"I have heard optometrists scoff at the idea of measuring astigma- 
tism with the retinoscope to the small amount of a quarter of a 
diopter, but such scoffing only proves that the party is not a user of 
the retinoscope, or certainly has not acquired skill in diagnosing errors 
with it. To me it is of great value in differentiating ^ diopter, or 
even less, of astigmatism, when unable to do it for a certainty with 
the trial case. 

"Fourthly — It measures the dioptric system as a whole — not the 
<cornea only, like the ophthalmometer. 

"I believe in the subjective trial-case test. I presume it will 
always remain an important test and probably the 'court of last resort,' 
"but the little retinoscope is a mighty power in the hands of the re- 
fractionist in difficult cases. With it and a practical knowledge of 
dynamic skiametry he has an equipment that will prove of immense 
-value. Without it he is distinctly at a disadvantage when he meets 
adverse conditions." 

Ciias. A. Jarvis, in Kansas City Jeweler, says : 

"The real value of dynamic retinoscopy lies in its ability to un- 
cover latent hyperopia. It is invariably successful in cases where a 
physician would use a cycloplegic. For instance, if rotation of the 
mirror shows no perceptible movement at first, and when a plus lens 
is placed before the eye under examination and the movement is not 
against the mirror then we may take it that the accommodation has 
relaxed to accept the plus lens. The power of that lens which can be 
retained before the eye without causing the shadow to move against 
the mirror is the amount of latent hyperopia." 

Under the caption of "Hozv Mydriatics act in Skiascopy/' 
Mr. L. G. Amsden, the well-known editor of the Canadian 
Optician, in the issue for April, 1910, says: 

"I am frequently in receipt of inquiries regarding the value of 
retinoscopy without the aid of a mydriatic, such queries being un- 
doubtedly prompted by the fool statements made in text-books, usually 
written by medical men, in which the stereotyped phrase is always 
found : The test is, of course, impossible and unreliable without the 
use of the mydriatic.' 



MENTAL PERCEPTION 213 

"Now, the truth is — and it is becoming generally recognized — that 
accurate results are impossible in retinoseopy when a mydriatic is used, 
owing to the fact that the enlarged pupil brings under examination 
certain parts of both cornea and lens that are not used under ordinary 
conditions, and which may possess curvature of an entirely different 
nature to that used in regular vision." 

A. S. Haskins, Treasurer A. O. A., in the Optical Journal 
of May 5, 1910, says : 

"Much is being written regarding subjective and objective optom- 
etry. Generally, little favor is given the latter. The same ones who* 
speak against objective optometry are among those who believe that 
20 years will show great advancement in optometry. Certainly, if" 
optometry advances it must be along objective lines. Much of this- 
predicted advancement will be the mastery of the present objective- 
methods by the ones who, to-day, think so little of them." 



MENTAL PERCEPTION. As having a bearing upon. 
the question of the relative value of subjective and objective 1 
optometry, a short consideration of the subject of mental per- 
ception, in general, may emphasize certain points showing why- 
it is unwise for optometrists to rely implicitly upon subjective 
data alone, extracts will therefore again be made from the 
pages of James' Briefer Psychology, in which he says : 

"Anything which affects our sense-organs does also more 
than that : it arouses processes in the hemispheres which are 
partly due to the organization of that organ by past experiences, 
and the results of which" in consciousness are described as ideas 
which the sensation suggests. The first of these ideas is that 
of the thing to which the sensible quality belongs. The con- 
sciousness of particular material things present to sense is 
nowadays called perception. The consciousness of such things 
may be more or less complete ; it may be of the mere name of 
the thing and its other essential attributes, or it may be of the 
thing's various remoter relations. It is impossible to draw any 



wmm^t^m 



214 MENTAL PERCEPTION 

sharp line of distinction between the barer and the richer con- 
sciousness, because the moment we get beyond the first crude 
sensation all our consciousness is of what is suggested, and the 
various suggestions shade gradually into each other, being one 
and all products of the same psychological machinery of asso- 
ciation. In the directer consciousness fewer, in the remoter 
more, associative processes are brought into play. 

"Every concrete particular material thing is a conflux of 
sensible qualities, with which we have become acquainted at 
various times. Some of these qualities, since they are more con- 
stant, interesting, or practically important, we regard as essen- 
tial constituents of the thing. In a general way, such are the 
tangible shape, size, mass, etc. Other properties, being more 
fluctuating, we regard as more or less accidental or inessential. 
We call the former qualities the reality, the latter its appear- 
.ances. Thus, I hear a sound, and say a 'horse-car' ; but the 
sound is not the horse-car, it is one of the horse-car's least 
important manifestations. The real horse-car is a feelable, or 
at most a feelable and visible, thing which, in my imagination, 
the sound calls up. So when I get, as now, a brown eye- 
picture with lines not parallel, and with angles unlike, and call 
it my big solid rectangular walnut library-table, that picture is 
not the table. It is not even like the table as the table is for 
vision, when rightly seen. It is a distorted perspective view 
of three sides of what I mentally perceive (more or less) in its 
totality and undistorted shape. The back of the table, its square 
corners, its size, its heaviness, are features of which I am con- 
scious when I look, almost as I am conscious of its name. The 
suggestion of the name is of course due to mere custom. But 
no less that of the back, the size, weight, squareness, etc. 

"Another well-known change is when we look at a land- 
scape with our head upside down. Perception is to a certain 
extent baffled by this manoeuvre; gradations of distance and 
mother space-determinations are made uncertain; the repro- 



MENTAL PERCEPTION 215 

ductive or associative processes, in short, decline ; and, simul- 
taneously with their diminution, the colors grow richer and 
more varied, and the contrasts of light and shade more marked. 
The same thing occurs when we turn a painting bottom up- 
ward. We lose much of its meaning, but, to compensate for 
the loss, we feel more freshly the value of the mere tints and 
shadings, and become aware of any lack of purely sensible 
harmony or balance which they may show. Just so, if we lie 
on the floor and look up at the mouth of a person talking 
behind us, his lower lip here takes the habitual place of the 
upper one upon our retina, and seems animated by the most 
extraordinary and unnatural mobility which now strikes us 
because (the associative processes being disturbed by the un- 
accustomed point of view) we get it as a naked sensation and 
not as part of a familiar object perceived. 

"There is a whole batch of illusions which come from 
optical sensation interpreted by us in accordance with our 
usual rule, although they are now produced by an unusual 
object. The stereoscope is an example. The eyes see a picture 
apiece, and the two pictures are a little disparate, the one seen 
by the right eye being a view of the object taken from a point 
slightly to the right of that from which the left eye's picture is 
taken. Pictures thrown on the two eyes by solid objects 
present this sort of disparity, so that we react on the sensation 
in our usual way, and perceive a solid. If the pictures be ex- 
changed we perceive a hollow mould of the object, for a hollow 
mould would cast just such disparate pictures as these. Wheat- 
stone's instrument, the pseudoscope, allows us to look at solid 
objects and see with each eye the other eye's picture. We then 
perceive the solid object hollow, // it be an object which might 
probably be hollozv, but not otherwise. Thus the perceptive 
process is true to its law, which is always to react on the sensa- 
tion in a determinate and figured fashion if possible, and in as 
probable a fashion as the case admits. 



2l6 EPILOGUE 

"Visual feeling of movement is produced by any image 
passing over the retina. Originally, however, this sensation is 
definitely referred neither to the object nor to the eyes. Such 
definite reference grows up later, and obeys certain simple laws. 
For one thing, we believe objects to move whenever we get the 
retinal movement-feeling, but think our eyes are still. This 
gives rise to an illusion when, after whirling on our heel, we 
stand still; for then objects appear to continue whirling in the 
same direction in which, a moment previous, our body actually 
whirled. The reason is that our eyes are animated, under these 
conditions, by an involuntary nystagmus, or oscillation in their 
orbits, which may easily be observed in anyone with vertigo 
after whirling. As these movements are unconscious, the retinal 
movement-feelings which they occasion are naturally referred 
to the objects seen. The whole phenomenon fades out after a 
few seconds, and it ceases if we voluntarily fix our eyes upon 
a given point. 

"No sense gives such fluctuating impressions of the same 
object as sight does. With no sense are we so apt to treat the 
sensations immediately given as mere signs ; with none is the 
invocation from memory. of a thing, and the consequent per- 
ception of the latter, so immediate. The 'thing' which we per- 
ceive always resembles the object of some absent sensation, 
usually another optical figure which in our mind has come to 
be a standard bit of reality ; and it is this incessant reduction of 
our immediately given optical objects to more standard and 
'real' forms which has led some authors into the mistake of 
thinking that our optical sensations are originally and natively 
of no particular form at all." 

EPILOGUE. Now, judging from the tenor of those 
articles which adversely criticise Dynamic Skiametry, it seems 
plain that their authors do not grasp the fact that the addition 
of plus spheric lenses causes accommodation to be relaxed in- 



EPILOGUE 217 

stead of taxed, and that a myopic eye under convergence shows 
more myopia than it does under relaxation, or while trying to 
see at a distance. 

An emmetropic eye, with an abundance of amplitude, in 
looking at an object 13 inches away exerts 3. D. of 
accommodation. If a minus 1. D. S. lens is added, the 
accommodation called for is 4. D., but if a plus 1. D. S. lens 
is added, in place of the minus 1. D., the eye will not relax 
to 2. D., and this is because of the correlation of convergence. 
If marked esophoria is present this may not hold true, but 
whatever relaxation does take place it will be the required 
refractive assistance necessary to harmonize accommodation 
with convergence at this distance, which, after all, is the data 
in the case that the optometrist is looking for. Then if the 
case will not finally accept any hyperopic correction for infinity 
it shows that a disturbed relationship between accommodation 
and convergence is present and that heterophoria or sub-normal 
ciliary duction may be factors. 

In a myopia of 1. D. convergence is not exerted while the 
eye is trying to look at infinity, but when fixation is at 40 inches 
convergence is then exerted 3 degrees, and this exertion un- 
questionably influences accommodation. 

Once more let it be stated that dynamic skiametry is not the 
whole of optometry, but that it gives an examiner valuable data 
that can not be obtained by any other known method. 

Optometry covers the measurement of the strength and 
tendencies of the extrinsic muscles as well as the strength and 
tendencies of the intrinsic ones, all of which must be taken into 
consideration. Testing amplitude of accommodation and ampli- 
tude of convergence is very different from determining the 
refractive assistance an eye will readily accept for different 
points of fixation. 

"Rules of thumb" are not always to be relied upon in 
optometry, for ocular conditions must be proven by various 



2lS EPILOGUE 

measurements, and then, after all possible data is obtained, 
trained judgment is called for, as an eye may show a different 
measurement for a six-meter distance than it does for a one- 
meter one, or for a third of a meter, and there is a reason for 
this variation if an examiner is well enough informed to as- 
certain it. Dynamic skiametry is merely one method that is 
given to aid in the solution of the all-important question: 
What lenses should be prescribed? 

Why other methods than subjective ones are needed in suc- 
cessful optometry may be readily inferred from the quotations 
on mental perceptions, here given, for in practical optometry all 
•experienced examiners know the great variety of answers a 
given question, such as "which line is the blackest?" will call 
forth from different patients. Independent information that 
will serve to "check up" a patient's carelessness, stupidity or 
misinterpretation of a question is, therefore, no longer optional 
in optometry, but, on the contrary, very vital to its theory and 
practice and to its forward movement as a profession, to which, 
it is hoped, dynamic skiametry materially contributes. 



INDEX 



Page 

A serious profession 122 

A simple experiment in 

magnifying 151 

A simple skiascope 40 

Abduction 112 

Absorption of spasm 88 

Abuse of lamps 35 

Accommodation and con- 
vergence in emmetropia.. 104 
Accommodation and _ con- 
vergence in hyperopia 106 

Accommodation and con- 
vergence in myopia 107 

Accommodation, subnormal. 120 

Accommodative myopia. ... 86 

Acetylene lamps 30 

Action of shadow 75 

Adduction 112 

Adequate illumination 22 

Adjustment of lamp 23 

"Against the mirror" 68 

Alcohol lamps 34 

Amplimetric 146 

Amplifying method 139 

Amplitude of accommoda- 
tion 132 

Amsden L. G. 212 

Apparent light source 19 

Appearance of shadow 69 

Argand lamps 30 

Arrows 104 

Artificially created errors.. 50 

" myopia. . 85 

As a system 15 

Asbestos covered lamps 36 

Asbestos chimneys 31 

Astigmia, regular and ir- 
regular 117 

Astigmatic dial 92 

Atkinson, T. G 205 

Author's lamp 36 

fixation stand 92 

skiameter 169 

skiascope 41 

record blank 145 

Balance of accommodation 

and convergence 104 

Behavior of shadow 67 



Page 

Binocular fixation 140 

trial set 156 

vision 104 

Black velvet 60 

Blind leading the blind.... 139 

Body tilting method 43 

Bowman, Sir. William Pa- 
get 3 

Bracket skiascope 41 

Breaking up of habits no 

Bright reflex 94 

Brow cards 42 

Burnett, Swan M 68 

Calcium carbide 31 

Candle power 23 

Captain of the visual ship... 83 

Card-board model 69 

Card illumination 61 

Careless examiners 149 

Carelessness of patients.... 218 

Case records 146 

Cases illustrative 124 

Chimney covers 33 

Ciliary spasms 108 

Cleaning the skiascope 40 

Clonic spasms 108 

Co-incident motion 67 

Color of shadow 25 

Combining of lenses 52 

Cook, H. J 206 

Compound errors 70 

Concave mirrors 39 

Conjugate foci 68 

Contents 7 

Contraction of muscles 108 

Cortical cataract 131 

Convergence interfered with 194 
Corroborative measure- 
ments 141 

Cost of maintenance of 

lamp 31 

Crain's disc 159 

Created myopia 85 

Crossing point of emer- 
gent says 66 

Crowding on plus lens 

quantity 04 

Crystalline lens 88 



■Mi 



HMMB 



INDEX— Continued 



Page 

Cuignet 5 

Cul-de-sac 138 

Cycloplegics 140 

Cylindric equivalents 61 

Deaf persons 149 

Decomposition of carbon 

filament 36 

Demarcation of light and 

shadow 64 

Devolopment of skill 116 

DeZeng's electric retino- 

scope 37 

DeZeng's optometer, phoro- 

meter and skiameter.... 167 
DeZeng's standard's Sche- 
matic eye 48 

Difference in "does" and 

"ought to" 67 

Different measurements.... 142 

Difficulties to be overcome. 21 

of skiametry. . . . 21 

Disputing the count 42 

Donder's rules 132 

Double bracket skiascope... 41 

Duction tests 122 

Dull reflexes 76 

Dynamic skiametry in the- 
ory 80 

Dynamic skiametry in prac- 
tice 134 

Economic stand-point 140 

Elastic bands 82 

Electric retinoscope 37 

Emergent rays 68 

Enlargement by magnifica- 
tion 150 

Epilepsy 108 

Epilogue 216 

Equal innervation 105 

Examination rooms 27 

Examiner's nodal point.... 42 

own vision .... 25 

Experience 115 

Extrinsic muscles 114 

Facial light _ 66 

False myopia 83 

Fifty candle power lamps.. 35 



Page 

Filament in lamps 34 

Final calculations 137 

First mate convergence.... 83 

Fixation 90 

" cards 93 

" stand 92 

position 94 

Fixed rules unreliable 217 

Formulas 54 

Forty-inch crossing point. . 84 

Fundus reflex 88 

Gas lamps 29 

General health 124 

Geneva retinoscope 164 

Glass chimneys 32 

Glory-hole 22 

Guessing 109 

Habit in convergence in 

" influence of 101 

Handle of skiascope 40 

Handling the skiascope.... 43 

Hardy's wall bracket 42 

Haskins, A. S 213 

Hartridge 81 

Harmonious convergence.. 104 

Head of author's skiameter 171 

Heat of lamps 35 

Heterophoric condition.... 100 

History 146 

Holding the skiascope 43 

Ideal conditions 27 

Illiterates 149 

Illumination 28 

Illuminated fundus 65 

Illuminating the fundus.... 64 

Illustrations, list of 9 

Illustrative cases 124 

Imbalance of accommoda- 
tion 106 

Imitation of shadow 69 

Improper examination 

rooms 27 

Increase in electric current 36 
Increased convexity of the 

crystalline 88 

Infinity 194 



INDEX— Continued 



Page 

Influence of brightness 22 

" habit 101 

Innervation 105 

in emmetropia 105 

hyperopia. . 106 

" moypia ... 107 

Initial examination 92 

Instruments as tools 153 

Instrument of Standart. . . . 160 

" Meriden ... 162 

" Geneva .... 164 

" DeZeng ... 167 

" Author .... 171 

Intensity of illumination... 22 
Involuntary contraction of 

muscles 108 

Irregular astigmia 117 

Iris diaphragm 33 

Jackson, Edward 168 

Jarvis, Chas. A 212 

Judgment in examination.. 218 

Keratometric 174 

Klein's retinoscope 46 

King's binocular trial set. . 156 

Knowledge necessary 18 

Kratometric 147 

Lamps Acetylene 30 

Argand 30 

" Gas 30 

" Electric 34 

" DeZeng's 37 

" Welsbach 32 

Latent errors 108 

Latent hyperopia 108 

Law of conjugate foci 68 

Law of light 22 

Lens values 51 

" reduction 55 

" < transposition 56 

Lenticular myopia 86 

"Lockwood, R. M 204 

Luminous retinoscope 37 

Macroscopically 51 

Magnification of pupil .... 150 

Mal-attached muscles 112 

Measuring astigmia 115 

presbyopia — 118 



Page 

Mechanical mydriasis 149 

Median line 104 

Mental perception 213 

Meriden oculometroscope.. 162 

Metal chimneys 31 

Metre angle 81 

Microscopically 51 

Mirrors 23 

Mixed astigmatic condition 50 

Mixed errors 50 

Mixed muscle action 100 

Mobile lens action 154 

Model eyes of metal 48 

" " pasteboard . 54 

Moore, H. B 200 

Multiple cards 42 

" fixation 91 

" methods 138 

Muscle balance in emme- 
tropia 104 

Muscle balance in hypero- 
pia 106 

Muscle balance in myopia.. 107 

innervation 105 

Muscular insufficiencies . . . 105 

Mydriatics 149 

Myopia, true and artificial. 84 

accommodative . . 86 

Nervous energy 101 

" impulses 101 

Neutralization at long range 51 

Neurometer 104 

Nodal point 42 

Non-luminous objects 60 

Non-toxic skiametry 139 

Normal relationship of ac- 
commodation and con- 
vergence 104 

Novel skiascopes 45 

Objective vs. subjective op- 
tometry 213 

Ocular fundus 65 

" skiametry as a sys- 
tem 15 

Oculometroscope 162 

Ocular pupils 151 

Oil lamps 29 

One to three relationship.. 81 



INDEX— Continued 



Page 

Opinions of others 197 

Optical knowledge neces- 
sary 18 

Optometer* of DeZeng 167 

Orthophoria and Hetero- 

phoria 100 

Other tests 121 

Parallelism of rays 66 

Paralleled rays of light 

converged 20 

Parent 157 

Partially deaf persons .... 149 

Peep holes 23 

Penumbra double 78 

in skiametry ... 79 

single 77 

Perception 213 

Phacometric 146 

Phorometer of DeZeng. . . . 167 

Phorometric 147 

Pigmentation 73 

Pink translucent paper.... 69 

Piano skiascope 39 

Point of reversal 66 

Position of light and mir- 
ror in skiametry 94 

Pound weight 80 

Practice of dynamic ski- 
ametry 115 

Preface 5 

Prentice, Charles F 3 

Presbymetric 147 

Presbyopia by skiametry... 119 

Prisms 133 

Principles of the author's 

skiameter 170 

Prismometric 147 

Proper rooms 27 

Pupils, large and small... 150 

" why they are red. . 60 

Quack doctor . . 51 

Queen's schematic eye 49 

Question and answers 173 

Quickness of shadow 74 

Ray bending power 53 

Rays direct 61 

" rellected 62 



Page 

Ray values 95 

Recognition of ability 59' 

Record blank 145 

Records 144 

Red pupils 60 

Reduction of lenses 51 

Re-education of converg- 
ence and accommodation 107 

Regular astigmia 117 

Keisner's retinoscope 45. 

Relation of accommodation 

and convergence 81 

Relationship of extrinsic 

and intrinsic muscles.... 81 

Relaxed accommodation . . . 216 

Reliable fixation 90 

Research work 48' 

Resourcefulness 148 

Retinal illumination 63 

target 64 

Retinoscope of Geneva 164 

Retinoscopy ' . 5 

Reversal of shadow 69^ 

Rheostats 36 

Risley's moble prism 154 

Scar tissue 117 

Schematic eyes 48' 

eye adjustment. 50 

eye practice.. 47 

Scissors movement 118 

Segements 147 

Shadow actions 67 

" measuring 69 

Shadow's imitation 69 

Shadow phenomena 6$. 

Size of retinal shadow.... 77 

" " skiascopic mirror. 39 

Skiascopes A3 

Skiameter of the author.... 171 

Skiametry as a system 15 

Skiametry, its value in op- 
tometry 16 

Skill 47 

Slader, A. R 209 

Sliding motion 155 

Slow shadows 75 

Snap switch 35 

Space for examination 27 

Sources of illumination .... 28 



INDEX— Continued 



Page 

Spasmodic muscle action . . 108 

Spasm of accommodation. . 89 

Spiral filament 34 

Stammer, A .W 197 

Standart's umbrameter. . . . 160 

Static method 70 

Straight line mirror move- 
ment 43 

Stumbling blocks 23 

Subjective optometry 109 

Sub-normal accommodation 120 

Sub-phenomena 73 

Synchronous 76 

Systematic case records.... 144 

System of ocular skiametry 16 

Theoretic skiametry 69 

Theories regarding dull re- 
flexes 73 

Theory of dynamic skiam- 
etry 80 

Tension of accommodation in 
" on extrinsic and in- 
trinsic muscles 106 

Tonic spasms 108 

Toxic skiametry 138 

Transposition of lenses.... 56 

Trial case last 142 

Tropometric 147 

True myopia 84 



Page 

Umbrameter of Standart. . 160 

Unconscious habits 101 

muscle effort.. 108 

Unequal innervation 106 

Unit lens action 156 

Units 51 

Use of instruments 157 

Value of instruments 153 

" " skiametry 17 

Various instruments used 

in skiametry 157 

Various skiascopes 39 

Visible objects 60 

Visibility of fundus 65 

Visual 90 

Visual fixation 106 

Voltage 35 

Voluntary muscle action... 104 

Wall bracket 38 

Wambold, F. A 198 

Welsbach lamps 32 

Why the pupil appears red 60 

''With the mirror" 67 

Wood alcohol 34 

Working lens 71 

Wiirdenmann's lens rack. . 158 



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